U.S. patent number 5,010,399 [Application Number 07/379,751] was granted by the patent office on 1991-04-23 for video transmission and control system utilizing internal telephone lines.
This patent grant is currently assigned to Inline Connection Corporation. Invention is credited to Robert Domnitz, David D. Goodman.
United States Patent |
5,010,399 |
Goodman , et al. |
April 23, 1991 |
Video transmission and control system utilizing internal telephone
lines
Abstract
A video transmission system for facilitating transmission of
video and control signals, particularly infrared remote control
signals, between different locations in a residence using existing
telephone wiring. Simultaneous transmission of signals of both
types over active telephone lines is possible without interference
with telephone communications. Transmission succeeds without
requiring special treatment of the video signals beyond RF
conversion, despite signal attenuation inherent in transmission
over the telephone line media. Two or more video sources may be
tied into the system, and selected as desired. Remote control
signals generated in one room may be utilized without requiring a
clear line of sight between the remote control device and the
receiver.
Inventors: |
Goodman; David D. (Arlington,
VA), Domnitz; Robert (Lexington, MA) |
Assignee: |
Inline Connection Corporation
(Arlington, VA)
|
Family
ID: |
23498531 |
Appl.
No.: |
07/379,751 |
Filed: |
July 14, 1989 |
Current U.S.
Class: |
348/14.01;
348/14.12; 348/E7.05; 348/E7.051; 348/E7.053; 348/E7.081;
348/E7.085; 379/102.03; 379/90.01; 398/106 |
Current CPC
Class: |
H04H
20/81 (20130101); H04L 12/2803 (20130101); H04L
12/2838 (20130101); H04M 11/062 (20130101); H04N
7/104 (20130101); H04N 7/106 (20130101); H04N
7/108 (20130101); H04N 7/147 (20130101); H04N
7/18 (20130101); H04L 12/282 (20130101); H04L
2012/2845 (20130101); H04L 2012/2849 (20130101) |
Current International
Class: |
H04M
11/06 (20060101); H04N 7/14 (20060101); H04H
1/04 (20060101); H04H 1/08 (20060101); H04N
7/10 (20060101); H04N 7/18 (20060101); H04N
007/12 () |
Field of
Search: |
;379/53,54,64,65,90,102,104,105,96-98 ;358/85,194.1
;455/602,603,606,617 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Advertisement for a MasterMind Device; Aug. 1989; Author Unknown.
.
"Instant Network Rides on Phone Lines", Electronic Design, Aug. 6,
1987; Author Unknown. .
"Build This Carrier Current Receiver", Radio Electronics, Feb.
1989, pp. 55 et. seq. .
"Build This Carrier Current Audio Transmitter", Radio Electronics,
Jan. 1989, pp. 56, 58-61, 64; Author Unknown. .
Brochure for Teleconcepts Product; Author and Data Unknown. .
Brochure for TeleVideo Product; Author and Date Unknown. .
Brochure for Javelin J411 Product; Author and Date Unknown. .
Brochure for Remote Extender Product; Author and Date
Unknown..
|
Primary Examiner: Ng; Jin F.
Assistant Examiner: Chan; Wing F.
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak &
Seas
Claims
What is claimed is:
1. A communication system that includes an electronic switching
device that provides an interface to a telephone system, a first
port ordinarily used for connection of telephone equipment and an
apparatus located in a first area, said apparatus supplying a first
video signal, a second port ordinarily used for connection of
telephone equipment and a television receiver located in a second
area, the communication system further including a first two-wire
conductive path connecting said first port to said switching
device, and a second two-wire conductive path connecting said
second port to said switching device, the communication system
further including:
(a) a first electronic device located in said first area
including:
receiving means connected to said first apparatus, for receiving
said first video signal.
signal processing means for providing a second video signal, said
second video signal having a higher energy level than said first
video signal and substantially the same information content as said
first video signal, and
first transmitting means, connected to said first one of said
ports, for transmitting said second video signal onto the network,
said first transmitting means comprising first filtering means for
presenting a high impedance to signals whose energy is concentrated
at frequencies below the highest frequency used for communication
by ordinary telephone devices, while allowing said second video
signal to transmit substantially unaltered:
(b) a second electronic device located in said second area
including:
recovering means, connected to said second one of said ports, for
recovering said second video signal from the network, said
recovering means comprising second filtering means for presenting a
high impedance to signals whose energy is concentrated at
frequencies below the highest frequency used for communication by
ordinary telephone devices, while allowing said second video signal
to transmit substantially unaltered: and
second transmitting means, connected to said television receiver,
for transmitting said video signals to said television
receiver,
(c) a connecting device (52) interposed along said first 2-wire
conductive path, including:
a first low-pass filter for allowing signals at frequencies used by
ordinary telephone devices to transmit along said first path
unaltered while blocking signals transmitted at frequencies at
which the energy of said second video signal is concentrated,
said connecting device also being interposed along said second
2-wire conductive path, and including a second low-pass filter for
allowing signals at frequencies used by ordinary telephone devices
to transmit along said path unaltered while blocking signals
transmitted at frequencies at which the energy of said second video
signal is concentrated,
said connecting device further including a third conductive path
connecting said first conductive path and said second conductive
path, and including a high pass filter for blocking passage of
signals concentrated at frequencies used by ordinary telephone
devices, and enabling electrical energy of said second video signal
to pass substantially unaltered, for allowing transmission of said
second video signal from said first port to said second port, while
maintaining the separation of telephone communications signals
between said switching device and each of said first port and said
second port.
2. A communications system that includes a network of wiring, a
plurality of ports ordinarily used for connection of telephone
equipment to said network, and an interface to a telephone system,
said ports being located in different areas, said network
comprising a plurality of 2-wire conductive paths connecting said
ports to said interface, the communications system including a
first one of said ports and a first electronic device (1) located
in a first area, and a second one of said ports and a second
electronic device (15) located in a second area, the system further
including an apparatus (2) located in said first area, said
apparatus responding to infrared light signals received from an
infrared light transmitter for determining operational modes of
said apparatus, said apparatus being out of range of said light
transmitter when said light transmitter is located in the second
area, wherein:
(a) said second electronic device (15) further includes:
first converting means for converting infrared light radiation to a
first series of electrical impulses,
first representing means for representing said first series of
electrical impulses as a second series of electrical impulses,
information content of said second series being substantially the
same as the information content of said first series, substantially
all of the energy of said second series being concentrated at
frequencies above the highest frequency used for communication by
ordinary telephone devices, wherein said first representing means
includes:
means for creating a weighted average signal, said weighted average
signal being a weighted average of the energy level of said first
series of electrical impulses over a preceding time period of
predetermined length,
means for creating a first bi-level signal, said first bi-level
signal assuming a high state when the energy level of said first
series of electrical impulses exceeds said weighted average signal,
said first bi-level signal otherwise assuming a low state,
means for suppressing noise by creating a second bi-level signal,
said second bi-level signal assuming a high state whenever the
energy level of said first series of electrical impulses exceeds
said weighted average by a fixed factor at any time over a
preceding time period of fixed length, said second bi-level signal
otherwise assuming a low state, and
means for providing an RF carrier only when both said first
bi-level signal and said second bi-level signal are at the higher
of their two said levels;
said second electronic device (15) further including first
transmitting means, connected to said second one of said ports, for
transmitting said second series of electrical impulses onto the
network, said first transmitting means comprising first filtering
means for presenting a high impedance to signals whose energy is
concentrated at frequencies below the highest frequency used for
communication by ordinary telephone devices, while allowing said
second series of electrical impulses to transmit substantially
unchanged, and wherein
(b) said first electronic device (1) further includes:
first recovering means, connected to said first one of said ports,
for recovering said second series of electrical impulses from the
network wiring, said first recovering means comprising second
filtering means for presenting a high impedance to signals whose
energy is concentrated at frequencies below the highest frequency
used for communication by ordinary telephone devices, while
allowing said second series of electrical impulses to transmit
substantially unchanged,
second representing means for representing said second series of
electrical impulses as a third series of electrical impulses,
information content of said third series being substantially the
same as the information content of said second series, and
second converting means for converting said third series of
electrical impulses to infrared light radiation, said second
converting means creating a light pattern with substantially the
same characteristics as the light pattern created by the infrared
light radiation in the second area.
3. A communication system that includes a network of wiring, a
plurality of ports ordinarily used for connection of telephone
equipment to said network, and an interface to a telephone system,
said ports being located in different areas, said network
comprising a plurality of 2-wire conductive paths connecting said
ports to said interface, the communications system including a
first one of said ports and a first electronic device (1) located
in a first area, and a second one of said ports and a second
electronic device (15) located in a second area, the system further
including an apparatus (2) located in said first area, said
apparatus responding to infrared light signals received from an
infrared light transmitter for determining operational modes of
said apparatus, said apparatus being out of range of said light
transmitter when said light transmitter is located in the second
area, wherein:
(a) said second electronic device (15) further includes:
first converting means for converting infrared light radiation to a
first series of electrical impulses,
first representing means for representing said first series of
electrical impulses as a second series of electrical impulses,
information content of said second series being substantially the
same as the information content of said first series, substantially
all of the energy of said second series being concentrated at
frequencies above the highest frequency used for communication by
ordinary telephone devices,
first transmitting means, connected to said second one of said
ports, for transmitting said second series of electrical impulses
onto the network, said first transmitting means comprising first
filtering means for presenting a high impedance to signals whose
energy is concentrated at frequencies below the highest frequency
used for communication by ordinary telephone devices, while
allowing said second series of electrical impulses to transmit
substantially unchanged,
(b) said first electronic device (1) further includes:
first recovering means, connected to said first one of said ports,
for recovering said second series of electrical impulses from the
network wiring, said first recovering means comprising second
filtering means for presenting a high impedance to signals whose
energy is concentrated at frequencies below the highest frequency
used for communication by ordinary telephone devices, while
allowing said second series of electrical impulses to transmit
substantially unchanged,
second representing means for representing said second series of
electrical impulses as a third series of electrical impulses,
information content of said third series being substantially the
same as the information content of said second series, and
second converting means for converting said third series of
electrical impulses to infrared light radiation, said second
converting means creating a light pattern with substantially the
same characteristics as the light pattern created by the infrared
light radiation in the second area,
said communications system further comprising a television receiver
located in said second area, wherein said apparatus (2) in said
first area includes means for supplying a first video signal and
wherein:
(i) said first electronic device (1) in said first area further
includes:
receiving means, connected to said apparatus (2), for receiving
said first video signal, and
signal processing means for providing a second video signal, said
second video signal having a higher energy level than said first
video signal and substantially the same information content as said
first video signal, and
second transmitting means, connected to said first one of said
ports, for transmitting said second video signal onto the network,
said second transmitting means comprising third filtering means for
presenting a high impedance to signals whose energy is concentrated
at frequencies below the highest frequency used for communication
by ordinary telephone devices, while allowing said second video
signal to transmit substantially unaltered; and wherein
(ii) the electronic device (15) located in the second area further
includes:
second recovering means, connected to said second one of said
ports, for recovering said second video signal from the network,
said second recovering means comprising fourth filtering means for
presenting a high impedance to signals whose energy is concentrated
by ordinary telephone devices, while allowing said second video
signal to transmit substantially unaltered, and
third transmitting means, connected to said television receiver,
for transmitting one of
(1) said second video signal or
(2) an alternative video signal having substantially the same
information content as said second video signal to said television
receiver.
4. A system as defined in claim 3 wherein said first electronic
device (1) further includes means for blocking the energy of said
second video signal from transmission to said second representing
means.
5. A system as defined in claim 3, wherein:
substantially all of the energy of said first video signal is
concentrated at frequencies between 54 Mhz and 72 Mhz,
said signal processing means comprises amplification means for
amplifying said first video signal, so as to provide said second
video signal,
the degree of amplification of said amplification means is variable
and manually adjustable, and
said second transmitting means includes a 2-conductor cord, the
conductors of said cord including one of,
(1) systematic twists about each other, and
(2) metallic shielding
for reducing RF radiation emanating from said cord.
6. A communication system as defined in claim 3 wherein:
substantially all of the energy of said first video signal is
concentrated at frequencies below 6 Mhz,
said first electronic device (1) further includes a switch with at
least first and second settings,
said signal processing means included in said first electronic
device (1) comprises RF conversion means for translating said first
video signal to provide a translated signal whose energy is
concentrated at higher frequencies, and amplification means for
amplifying said translated signal to provide said second video
signal, said RF conversion means responding to the setting of said
switch to determine the frequencies at which the energy of said
second video signal is concentrated, substantially all of the
energy of said second video signal being concentrated at
frequencies between 76 Mhz and 82 Mhz when said switch is at said
first setting, and being concentrated at frequencies between 82 Mhz
and 88 Mhz when said switch is at said second setting.
7. A system as defined in claim 3 wherein:
said signal processing means included in said first electronic
device (1) comprises first RF conversion means for converting said
first video signal to a signal with a higher energy level whose
energy is concentrated at frequencies below 54 Mhz so as to provide
said second video signal,
said second electronic device (15) includes second RF conversion
means for converting signals within an input band to signals whose
energy is concentrated at frequencies above 54 Mhz so as to provide
a third video signal, said input band covering the frequencies of
said second video signal, said third video signal having
substantially the same information content as said second video
signal,
said third transmitting means connected to said television receiver
comprises means for transmitting said third video signal to said
television receiver.
8. A system as defined in claim 7 wherein:
said second electronic device (15) further includes adjusting means
with at least first and second settings, and
said second RF conversion means responds to the setting of said
adjusting means to determine the frequencies at which the energy of
said third video signal is concentrated, substantially all of the
energy of said third video signal being concentrated within a first
output band when said adjusting means is at said first setting, and
within a second output band when at said second setting, a width of
said first and the width of said second output bands being 6 Mhz,
said first output band being adjacent to and below said second
output band.
9. A system as defined in claim 7 wherein:
said second RF conversion means comprises means for simultaneously
providing both a supplemental video signal and said third video
signal, substantially all of the energy of said supplemental video
signal falling within a 6 Mhz supplemental band, substantially all
of the energy of said third video signal being confined within a 6
Mhz band below and adjacent to said supplemental band, said
supplemental video signal having substantially the same information
content as said third video signal, and
said third transmitting means connected to said television receiver
comprises means for simultaneously transmitting both said third
video signal and said supplemental video signal to said television
receiver.
10. A system as defined in claim 7 wherein:
substantially all of the energy of said first video signal supplied
by said apparatus (2) is concentrated within an initial band above
54 Mhz, the width of said initial band being at least 12 Mhz.
said first RF conversion means comprises means comprises means for
converting substantially all signals within said initial band to
signals at a higher energy level whose energy is concentrated
within an intermediate band below 54 Mhz, so as to provide said
second video signal within said intermediate band, said
intermediate band being equal in width to said initial band,
said second RF conversion means comprises means for converting
substantially all signals within said intermediate band to signals
whose energy is concentrated within said initial band, so as to
provide said third video signal within said initial band,
said initial band being composed of all of the frequencies between
one of:
(1) 60 Mhz and 72 Mhz, and
(2) 54 Mhz and 72 Mhz.
11. A system as defined in claim 7 wherein:
substantially all of the energy of said first video signal is
concentrated at frequencies below 6 Mhz, and
said first electronic device (1) further includes a switch with at
least first and second settings, and
said first RF conversion means responds to the setting of said
switch to determine the frequencies at which the energy of said
second video signal is concentrated, substantially all of the
energy of said second video signal being concentrated within a
first 6 Mhz intermediate band when said switch is at said first
setting, and within a second 6 Mhz intermediate band when said
switch is at said second setting said first intermediate band being
adjacent to and below said second intermediate band, and
said second RF conversion means comprises means for converting
substantially all signals within a third intermediate band to
signals whose energy is concentrated within an output band above 54
Mhz, so as to provide said third video signal within said output
band, said third intermediate band consisting of all frequencies
within said first and said second intermediate bands, the width of
said output band being equal to the width of said third
intermediate band.
12. A system as defined in claim 7 wherein:
said first RF conversion means comprises means for simultaneously
providing both a first supplemental video signal and said second
video signal, substantially all of the energy of said first
supplemental video signal being concentrated within a 6 Mhz
supplemental band, substantially all of the energy of said second
video signal being concentrated in a 6 Mhz band above and adjacent
to said supplemental band, said supplemental video signal having
substantially the same information content as said second video
signal,
said second transmitting means further comprises means for
simultaneously transmitting both said first supplemental video
signal and said second video signal onto the network,
said second RF conversion means comprises means for converting
substantially all signals within an intermediate band to signals
within an output band 54 Mhz, so as to provide said third video
signal and a second supplemental video signal within said output
band, said intermediate band consisting of the frequencies within
said first supplemental band and within the 6 Mhz immediately
above, said second supplemental video signal having substantially
the same information content as said first supplemental video
signal, and
said third transmitting means connected to said television receiver
comprises means for simultaneously transmitting both said third
video signal and said supplemental video signal to said television
receiver.
13. A communications system that includes a network of wiring, a
plurality of ports ordinarily used for connection of telephone
equipment to said network, and an interface to a telephone system,
said ports being located in different areas, said network
comprising a plurality of 2-wire conductive paths connecting said
ports to said interface, the communications system including a
first one of said ports and an apparatus (2) located in a first
area, said apparatus (2) supplying a first video signal, and a
second one of said ports and a television receiver located in a
second area, the communications system further comprising:
(a) a first electronic device (1) located in said first area
including:
receiving means, connected to said apparatus (2), for receiving
said first video signal;
first RF conversion means for converting said first video signal to
a signal whose energy is concentrated at different frequencies, so
as to provide a second video signal, substantially all of the
energy of said second signal being concentrated at frequencies
below 54 Mhz, information content of said second video signal being
substantially the same as information content of said first video
signal;
amplification means for amplifying said second video signal;
and
first transmitting means, connected to said first one of said
ports, for transmitting said second video signal onto the network,
said first transmitting means comprising first filtering means for
presenting a high impedance to signals whose energy is concentrated
at frequencies below the highest frequency used for communication
by ordinary telephone devices, while allowing said second video
signal to transmit substantially unaltered;
(b) a second electronic device (15) located in said second area
including:
recovering means, connected to said second of said ports, for
recovering said second video signal from said network, said
recovering means including second filtering means for presenting a
high impedance to signals whose energy is concentrated at
frequencies below the highest frequency used for communication by
ordinary telephone devices, while allowing said second video signal
to transmit substantially unaltered;
second RF conversion means for converting said second video signal
to a signal whose energy is concentrated at higher frequencies, so
as to provide third video signal, substantially all of the energy
of said third video signal being concentrated at frequencies above
54 Mhz, the information content of said third video signal being
substantially the same as the information content of said second
video signal; and
second transmitting means, connected to said television receiver,
for transmitting said third video signal to said television
receiver.
14. A system as defined in claim 13 wherein:
said second electronic device (15) further includes adjusting means
with at least first and second settings, and
said second RF conversion means responds to the setting of said
adjusting means to determine the frequencies at which the energy of
said third video signal is concentrated, concentrating
substantially all of the energy of said third video signal within a
first 6 Mhz output band when said adjusting means is at said first
setting, and within a second 6 Mhz output band when at said second
setting, said first output band being adjacent to and below said
second output band.
15. A system as defined in claim 13 wherein:
said second RF conversion means comprises means for simultaneously
providing both a supplemental video signal and said third video
signal, substantially all of the energy of said supplemental video
signal falling within a 6 Mhz supplemental band, substantially all
of the energy of said third video signal being concentrated within
a 6 Mhz band below and adjacent to said supplemental band, said
supplemental video signal having substantially the same information
content as said third video signal, and
said second transmitting means connected to said television
receiver comprises means for simultaneously transmitting both said
third video signal and said supplemental video signal to said
television receiver.
16. A system as defined in claim 13 wherein:
substantially all of the energy of said first video signal supplied
by said apparatus (2) is concentrated within an initial band above
54 Mhz, the width of said initial band being at least 12 Mhz,
said first RF conversion means comprises means for converting
substantially all signals within said initial band to signals whose
energy is concentrated within an intermediate band below 54 Mhz, so
as to provide said second video signal within said intermediate
band, said intermediate band being equal in width to said initial
band,
said second RF conversion means comprises means for converting
substantially all signals within said intermediate band to signals
whose energy is concentrated within said initial band, so as to
provide said third video signal within said initial band,
said initial band being composed of all of the frequencies between
one of:
(1) 60 Mhz and 72 Mhz, and
(2) 54 Mhz and 72 Mhz.
17. A system as defined in claim 13 wherein:
substantially all of the energy of said first video signal is
concentrated at frequencies below 6 Mhz,
said first electronic device (1) further includes a switch with at
least first and second settings,
said first RF conversion means responds to the setting of said
switch to determine the frequencies at which the energy of said
second video signal is concentrated, concentrating substantially
all of the energy of said second video signal at frequencies within
a first 6 Mhz intermediate band when said switch is at said first
setting, and within a second 6 Mhz intermediate band when said
switch is at said second setting, said first intermediate band
being adjacent to and below said second intermediate band, and
said second RF conversion means comprises means for converting
substantially all signals within a third intermediate band to
signals whose energy is concentrated within an output band above 54
Mhz, so as to provide said third video signal within said output
band, said third intermediate band consisting of all frequencies
within said first and said second intermediate bands, the width of
said output band being equal to the width of said third
intermediate band.
18. A system as defined in claim 13 wherein:
said first RF conversion means comprises means for simultaneously
providing both a first supplemental video signal and said second
video signal, substantially all of the energy of said first
supplemental video signal being concentrated within a 6 Mhz
supplemental band, substantially all of the energy of said second
video signal being concentrated in a 6 Mhz band above and adjacent
to said supplemental band, said first supplemental video signal
having substantially the same information content as said second
video signal,
said first transmitting means further comprises means for
simultaneously transmitting both said first supplemental video
signal and said second video signal onto the network,
said second RF conversion means comprises means for converting
substantially all signals within an intermediate band to signals
within an output band above 54 Mhz, so as to provide said third
video signal and a second supplemental video signal within said
output band, said intermediate band consisting of the frequencies
of said first supplemental band and the 6 Mhz immediately above,
said second supplemental video signal having substantially the same
information content as said first supplemental video signal.
19. A system as defined in claim 13 wherein:
said first RF conversion means comprises means for providing a
supplemental video signal in addition to said second video signal
so as to provide an alternative in the event that broadcast energy
interferes with said second video signal, substantially all of the
energy of said supplemental video signal being concentrated within
a 6 Mhz supplemental band different from the band of said second
video signal, said supplemental video signal having substantially
the same information content as said second video signal,
said second RF conversion means further comprises means for
converting substantially all signals within said supplemental band
to signals above 54 Mhz, so as to provide a second supplemental
video signal, the energy of said second supplemental signal being
concentrated within one of two adjacent 6 Mhz channels above 54
Mhz. said second supplemental video signal having substantially the
same information content as said first supplemental video
signal.
20. A system as defined in claim 13 wherein:
said second electronic device (15) further includes special
filtering means for filtering one of,
(1) said second video signal, and
(2) said third video signal, said special filtering means
attenuating signal energy at one of:
(1) frequencies between 4 Mhz and 4.5 Mhz above the picture
carrier, and
(2) frequencies within the 1.25 Mhz band immediately below the
picture carrier,
so as to reduce bandwidth, and so reduce a likelihood of
interference from broadcast signals.
21. A communications system that includes a network of wiring, a
plurality of ports ordinarily used for connection of telephone
equipment to said network, and an interface to a telephone system,
said ports being located in different areas, said network
comprising a plurality of 2-wire conductive paths connecting said
ports to said interface, the communications system including a
first one of said ports and an electronic device (1) located in a
first area, and a second one of said ports and a television
receiver (30) located in a second area, the system further
including an apparatus (2) located in said first area, said
apparatus (2) supplying a first video signal and responding to
infrared light signals received from a first infrared light
transmitter for determining the operational mode of said apparatus,
said apparatus being out of range of said light transmitter when
said transmitter is located in said second area, wherein:
(a) said electronic device (1) located in said first area
includes;
receiving means connected to said apparatus (2) for receiving said
first video signal;
signal processing means for providing a second video signal, said
second video signal having a higher energy level than said first
video signal and substantially the same information content as said
first video signal: and
first transmitting means, connected to said first one of said
ports, for transmitting said second video signal onto the network,
said first transmitting means comprising first filtering means for
presenting a high impedance to signals whose energy is concentrated
at frequencies below the highest frequency used for communication
by ordinary telephone devices, while allowing said second video
signal to transmit substantially unaltered;
(b) said television receiver (30) located in said second area
includes:
first recovering means, connected to said second one of said ports,
for recovering said second video signal from the network, said
first recovering means comprising second filtering means for
presenting a high impedance to signals whose energy is concentrated
at frequencies below the highest frequency used for communication
by ordinary telephone devices, while allowing said second video
signal to transmit substantially unaltered:
first converting means for converting infrared light radiation to a
first series of electrical impulses;
first representing means for representing said first series of
electrical impulses as a second series of electrical impulses,
information content of said second series being substantially the
same as the information content of said first series, substantially
all of the energy of said second series being concentrated at
frequencies above the highest frequency used for communication by
ordinary telephone devices: and
second transmitting means, connected to said second one of said
ports, for transmitting said second series onto the network, said
second transmitting means comprising third filtering means for
presenting a high impedance to signals whose energy is concentrated
at frequencies below the highest frequency used for communication
by ordinary telephone devices, while allowing said second series to
transmit substantially unaltered;
(c) said electronic device (1) located in said first area further
includes:
second recovering means, connected to said first one of said ports,
for recovering said second series of electrical impulses from the
network wiring, said second recovering means comprising fourth
filtering means for presenting a high impedance to signals whose
energy is concentrated at frequencies below the highest frequency
used for communication by ordinary telephone devices, while
allowing said second series to transmit substantially
unaltered;
second representing means for representing said second series of
electrical impulses as a third series of electrical impulses,
information content of said third series being substantially the
same as the information content of said second series, and
second converting means for converting said third series of
electrical impulses to infrared light radiation, said second
converting means creating a light pattern with substantially the
same characteristics as the light pattern created by the infrared
light radiation in the second area.
22. A communications system as set forth in claim 21, wherein:
said electronic device (1) further includes means for blocking the
energy of said second video signal from transmission to said second
presenting means.
23. A communications system as set forth in claim 21, further
including:
a second infrared light transmitter that includes means to control
the parameters of said television receiver and one of:
(1) means for issuing light patterns, other than those that control
the parameters of said television receiver (30), for determining
the parameters of other devices; and
(2) means for reissuing the light patterns of other infrared
transmitters designed to control other devices, after reception of
those patterns in a cooperative learning process with said other
infrared transmitters.
24. A communications system as set forth in claim 21. wherein:
said signal processing means included in said electronic device (1)
comprises first RF conversion means for converting said first video
signal to a signal with a higher energy level whose energy is
concentrated at frequencies below 54 Mhz, so as to provide said
second video signal.
25. A communications system as set forth in claim 24, wherein:
said television receiver (30) further includes special filtering
means for filtering said second video signal, said special
filtering means attenuating signal energy at one of:
(1) frequencies between 4 Mhz and 4.5 Mhz above the picture
carrier, and
(2) frequencies within the 1.25 Mhz band immediately below the
picture carrier,
so as to reduce bandwidth, and so reduce a likelihood of
interference from broadcast signals.
26. A communications system as set forth in claim 24, further
comprising processing means for processing said second video signal
to produce a third video signal, and wherein;
said television receiver (30) further includes special filtering
means for filtering said third video signal, said special filtering
means attenuating signal energy at one of:
(1) frequencies between 4 Mhz and 4.5 Mhz above the picture
carrier, and
(2) frequencies within the 1.25 Mhz band immediately below the
picture carrier,
so as to reduce bandwidth, and so reduce a likelihood of
interference from broadcast signals.
27. A communication system as set forth in claim 24, wherein:
said first RF conversion means further comprises means for
providing a supplemental video signal for the purposes of offering
an alternative in the event that broadcast interference disrupts
reception of said second video signal by said television
transceiver (30), substantially all of the energy of said
supplemental video signal being concentrated within a 6 Mhz wide
supplemental band, said supplemental band covering different
frequencies than the frequencies of said second video signal, said
supplemental video signal having substantially the same information
content as said second video signal, and
said first transmitting means further comprises means for
transmitting said supplemental video signal onto the network.
28. A communications system as set forth in claim 24. wherein:
said television receiver (30) further includes second RF conversion
means for converting said second video signal to a signal whose
energy is concentrated at different frequencies, so as to provide a
third video signal, and tuning means for tuning to signals above 54
Mhz, said tuning means being separate and distinct from said second
RF conversion means, said third video signal having the same
information content as said second video signal, substantially all
the energy of said third video signal being concentrated at one
of:
(a) frequencies above 54 Mhz, and
(b) frequencies below 6 Mhz.
29. A communications system that includes a network of wiring, a
plurality of ports ordinarily used for connection of telephone
equipment to said network, and an interface to a telephone system,
said ports being located in different areas, said network
comprising a plurality of 2-wire conductive paths connecting said
ports to said interface, the communications system further
including a first one of said ports and a first apparatus located
in a first area, said first apparatus providing a first video
signal, a second one of said ports and a second apparatus located
in a second area, said second apparatus providing a second video
signal, the energy of said first video signal concentrated at
substantially the same frequencies as the energy of said second
video signal, and a third one of said ports and a television
receiver located in a third area, said communications system
further comprising:
(a) a first electronic device located in said first area
including:
means, connected to said first apparatus, for receiving said first
video signal;
first signal processing means including a first amplifier for
providing a third video signal, said third video signal having a
higher energy level than said first video signal and substantially
the same information content as said first video signal:
first transmitting means, connected to said first one of said
ports, for transmitting said third video signal onto the network,
said first transmitting means comprising first filtering means for
presenting a high impedance to signals whose energy is concentrated
at frequencies below the highest frequency used for communication
by ordinary telephone devices, while allowing said third video
signal to transmit substantially unaltered,
(b) a second electronic device located in said second area
including:
means, connected to said second apparatus, for receiving said
second video signal;
second signal processing means including a second amplifier for
providing a fourth video signal, said fourth video signal having a
higher energy level than said second video signal and substantially
the same information content as said second video signal; and
second transmitting means, connected to said second one of said
ports, for transmitting said fourth video signal onto the network,
said second transmitting means comprising second filtering means
for presenting a high impedance to signals whose energy is
concentrated at frequencies below the highest frequency used for
communication by ordinary telephone devices, while allowing said
fourth video signal to transmit substantially unaltered;
(c) a third electronic device located in said third area
including:
recovering means, connected to said third one of said ports, for
recovering said third and fourth video signals from the network,
said recovering means comprising third filtering means for
presenting a high impedance to signals whose energy is concentrated
at frequencies below the highest frequency used for communication
by ordinary telephone devices, while allowing said third and said
fourth video signals to transmit substantially unaltered;
third transmitting means, connected to said television receiver,
for transmitting said third and fourth video signals to said
television receiver;
and wherein at least one of said first electronic device and said
second electronic device further includes one of;
(1) filter means having at least first and second operational
settings, for blocking transmission of electrical energy
concentrated within a particular frequency band to the network when
at said first operational setting, and permitting transmission of
electrical energy concentrated within said particular frequency
band to the network when at a second operational setting, said
filter means further including means for detecting DTMF (dual tone
multi-frequency) signals, said filter means adopting one of said
first and second operational settings in accordance with detection
of special sequences of DTMF signals and
(2) switching means including first and second operational modes,
said means preventing the supply of power to the amplifier included
in the electronic device that includes said switching means when at
a first operational mode, and permitting the supply of power to the
amplifier included in the electronic device that includes said
switching means when at a second operational mode. said switching
means further including means for detecting signals transmitted
across standard electrical power wiring and adopting said first or
said second operational mode in accordance with information
contained in said signals transmitted across said power wiring.
30. A communications system that includes a network of wiring, a
plurality of ports ordinarily used for connection of telephone
equipment to said network, and an interface to a telephone system,
said ports being located in different areas, said network
comprising a plurality of 2-wire conductive paths connecting said
ports to said interface, the communications system further
including a first one of said ports and a first apparatus located
in a first area, said first apparatus supplying a first video
signal, and a second one of said ports and a television receiver
located in a second area, said communications system further
including:
(a) a first electronic device located in said first area and
including:
receiving means, connected to said first apparatus, for receiving
said first video signal,
signal processing means for providing a second video signal, said
second video signal having a higher energy level than said first
video signal and substantially the same information content as said
first video signal, and
first transmitting means, connected to said first one of said
ports, for transmitting said second video signal onto the network,
said first transmitting means comprising first filtering means for
presenting a high impedance to signals whose energy is concentrated
at frequencies below the highest frequency used for communication
by ordinary telephone devices, while allowing said second video
signal to transmit substantially unaltered;
(b) a second electronic device located in said second area and
including:
recovering means, connected to said second one of said ports, for
recovering said second video signal from the network, said
recovering means comprising second filtering means for presenting a
high impedance to signals whose energy is concentrated at
frequencies below the highest frequency used for communication by
ordinary telephone devices, while allowing said second video signal
to transmit substantially unaltered; and
second transmitting means, connected to said television receiver,
for transmitting said second video signal to said television
receiver;
(c) wherein at least one of said first and second electronic
devices further includes:
a supplemental port for connecting ordinary telephone equipment,
and a path for transmission of electrical energy, said path
connecting between said supplemental port and one of said first and
second ports, said path including filter means for allowing energy
concentrated at frequencies used by ordinary telephone devices to
pass substantially unaltered while attenuating energy at
frequencies wherein the energy of said second video signal is
concentrated, said filter means diverting energy of said second
video signal away from said telephone equipment.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a system for transmitting signals
between components of a video system over the telephone wiring of a
residence.
Until the late 1970's, it was very unusual for ordinary consumers
to own electronic devices that generated or supplied video signals.
Virtually all video programs viewed on television sets were
received "over the air". This situation changed over the past
decade as VCRs, video cameras cable converters, and home satellite
systems became popular.
Currently, many consumers are able to watch video programs at
different locations because they own more than one television set.
When viewing programs from one of the sources mentioned above
rather than those picked up "over the air" however, it is necessary
to convey the signal from the video source to the television set.
When source and receiver are located in the same room, connecting
the two with a coaxial cable is usually the easiest method. VCRs
and cable converters are nearly always connected to nearby
television sets in this manner.
When the source and receiver are not located in the same area, a
network of coaxial cabling extending through the residence is a
fine solution. Most residences, however, are not wired this way, or
have networks that do not allow access at all desired locations.
Furthermore, most consumers insist that the wiring be neatly
installed or kept entirely out of sight making installation of a
network very difficult and unwieldy. This presents a problem when
connection between a video source and a television requires wiring
that extends between rooms, especially rooms located far from each
other, or on different levels.
Today, it is very common for a residence to include a VCR and a
television located in a "sitting room", and a second television
located in a bedroom. This has generated an enormous demand for
technology that transmits video across a residence without
requiring installation of new wires. Possible solutions are to
broadcast the signal at low power, or to use power lines or
telephone wiring, which are always available as a conductive
path
Broadcasting is currently not feasible in the U.S. because of FCC
regulations and is not feasible in most other countries for similar
reasons. (Several consumer devices that broadcast video at low
power have been marketed, however, despite their clear violation of
FCC regulations. This testifies to the existence of a large demand
for transmission of video over short distances.) In addition to
legal obstacles, the possibility of unintended reception of
broadcast signals outside residences and the possibility of
interference from other sources broadcasting at the same frequency
also present problems.
Regulations covering transmission between source and receiver over
conductive paths are much less restrictive and signals transmitted
by this method are much less likely to encounter interference from
other signals or be open to interception. Transmission across power
wiring is very difficult, however because appliances typically
attached to those networks often impart electrical noise at many
different radio frequencies creating a high potential for
interference. Furthermore, a reliable conductive path is not always
available across "fuse boxes", causing problems when source and
receiver derive power from different circuits.
The difficulties in transmitting video by broadcasting or by
conduction over power lines leave conduction over telephone wiring
as the sole remaining option. This technique also involves very
serious technological and legal challenges, however, and no
solution has been found.
The most obvious difficulties are avoiding interference with
telephone communications and conforming with all regulations that
govern devices that connect to the public telephone network.
Because telephone wiring in the US and many other countries
typically includes four conductors only two of which are used for
communications in residences served by a single telephone number,
availability of the unused pair would seem to present an
interesting opportunity for avoiding these problems. Unfortunately,
wiring installers often do not connect the unused pair at the
network junctions leaving breaks in the conductive paths offered by
these wires.
The path supplied by the active pair, on the other hand is
guaranteed to be continuous between two jacks as long as telephone
devices become active when connected at those jacks. An exception
is residences where each jack is wired directly to a central
electronic switching unit that provides an interface to the public
telephone system. The conductive paths between jacks are likely to
be broken across this unit.
There are other technical and legal problems associated with
transmission over this wiring beyond those created by the
connection to a public or private telephone network. The technical
problems derive from the fact that transmission of video was not a
consideration when standards for wire properties installation and
connection techniques, and telephone electronics were established.
Because these are all factors that can influence the ability of the
wiring to reliably transmit high quality RF signals, this
environment is poorly suited for transmission of video.
Further legal problems derive from the fact that all RF signals
conducted across unshielded wiring will broadcast at least some
electromagnetic radiation. (Unlike coaxial cable, telephone wiring
is not shielded by a grounded metallic conductor that eliminates
radiation.) Because restrictions on RF radiation are very limiting
in the US and most other countries they can potentially defeat any
particular electronic technique that could otherwise successfully
achieve transmission.
Systems have been developed to transmit video signals over ordinary
telephone wiring but none is practical for the residential
application described Chou (U.S. Pat. No. 4,054,910) discloses a
system for transmitting video over an ordinary pair of wires
without boosting the video signal in frequency. Video signals
transmitted by devices that follow that design, however, would
include energy at low frequencies that would interfere with
telephone signals.
Tatsuzawa (U.S. Pat. No. 3,974,337) discloses a system that
slightly boosts video signals in frequency (by approximately 0.5
Mhz) to prevent conflict with voiceband communications. The system
also requires, however, a sophisticated procedure for compressing
the bandwidth of the signal so as to avoid use of energies at the
higher frequencies, which attenuate quickly. Further, the higher
end of the resulting band is "preemphasized", or amplified more
than the lower frequencies, in order to account for the remaining
differences in attenuation.
The purpose of the technique disclosed by Tatsuzawa is to allow
video signals to travel distances on the order of 1 km or more. The
electronics that reduce and expand the signal bandwidth however,
are very expensive. There is also a major difficulty in that the
preemphasis of the signal must be adjusted depending on the
distance between source and receiver. This is of significant
inconvenience to a consumer. Further, the system depends on
electrical characteristics particular to frequencies between 0 and
4 Mhz limiting the transmission frequency to that band. This
creates legal problems because in the U.S.. for example,
regulations severely limit the RF energy below 6 Mhz that can be
fed to wiring that is connected to the public telephone network
Finally, the restriction to a single band allows for transmission
of only a single signal. There are countless methods for reducing
the resolution or the refresh rate of a video signal in order to
reduce the bandwidth enough to avoid the problem of attenuation,
e.g. Lemelson (U.S. Pat. No. 4,485,400). Current video standards in
the U.S. and elsewhere, however, use a refresh rate just quick
enough to avoid annoying "flickering" of the picture. Because most
consumers have little tolerance for "flickering" or a reduced
picture quality, these techniques do not present solutions to the
problem at hand.
Two commercially available devices are known by the inventors to
transmit uncompromised video across telephone wiring. The first
device is marketed by several cable equipment supply companies,
e.g. the J411 system marketed by Javelin Electronics of Torrance,
CA. The list price of this device is nearly $1000.
The device transmits a single unmodulated video signal across the
wiring. Because some of the energy of these signals is concentrated
at frequencies below 3 khz the device will cause interference with
telephone communications. Further, the specifications stipulate
that "transmission must be via dedicated twisted pair (of which
telephone wiring is a subset) and must be clean, unloaded, and
unconnected to any other device." The device also "pre-emphasizes"
the signal by imparting more amplification at the higher
frequencies, adding expense and the inconvenience of requiring
adjustment on the part of the user.
The second device, "Tele-Majic," is marketed by Impact 2000. a
catalog specializing in consumer electronic devices. This device is
composed of a pair of identical connecting cables. These cables are
advertised as enabling one to connect a video source to a
residential telephone line in one area and a television receiver in
a second area, for the purpose of viewing the source at the second
location.
Each cable consists of a classic matching transformer which
connects to the video devices a capacitor for blocking telephone
signals to prevent interference, and a telephone cord terminated
with a "male" RJ-11 plug, the standard plug for connection to a
telephone jack.
The device is intended to work by simply feeding the video signal
from the source on to the wiring and recovering it at a remote
location. For several reasons, it does not nearly solve the problem
at hand.
To begin with because "Tele-Majic" does not provide a video
amplifier, the strength of the signal fed to the wiring will be
limited by the strength of the signal supplied by the source. This
causes a problem because the output signal levels generated by VCRs
sold in the U.S. are limited by law to approximately 10 dB re 1 mV
into 75 ohms. At this level, the video signal can transmit only a
few feet before the wiring will attenuate its energy below the
level required for quality television reception.
Beyond the limitations caused by low signal power, the matching
transformer of the "Tele-Majic". which constitutes half of the
electronics in the device, is significantly suboptimal, and does
not teach anything about the correct purpose of that component. In
an apparent attempt to economize the common 75 ohm/300 ohm matching
transformer, built to connect between 75 ohm coaxial cabling and
"twin-lead" wiring was chosen. Because matching transformers of the
same design are included with virtually every video device sold in
the U.S., these are extremely inexpensive to obtain.
A matching transformer can serve the purpose of matching the
impedance of video equipment to telephone wiring. The impedance of
typical telephone wiring, however is approximately 100 ohms at low
VHF channels, not 300 ohms. This will create an impedance mismatch,
and video signals will lose more energy than is necessary when
passing from the source onto the network via this cable.
The transformer can also serve the purpose of balancing the
voltages on the two leads of the telephone wiring, in order to
reduce electromagnetic radiation. Because the transformer used by
"Tele-Majic" is designed to handle signals at all video
frequencies, however, it cannot balance the video signal nearly as
well as a transformer specifically tailored for a specific
frequency. The lack of balance will cause more radiation than would
be released by a maximally balanced signal.
Another problem is that complete isolation of telephone signals
using the particular transformer supplied with the device requires
two capacitors rather than the single one which comes with
"Tele-Majic". This design flaw will cause total disruption of
telephone communications when the device is connected to a coaxial
port whose outer shield connects to ground.
Given the ability to transmit video signals throughout a residence,
the viewer of signals at a remote television remains limited in the
ability to control the apparatus that supplies the signal. Many
video sources, especially VCRs and cable converters, are designed
to cooperate with hand-held controllers that send out infrared
control signals upon command of the user. Unfortunately signals
from these devices do not travel between rooms unless there is a
line-of-sight path between transmitter and source. It follows that
a significant demand for transmission of control signals should
arise as a result of technology that succeeds in transmitting video
across telephone wiring. Furthermore, there is an obvious economy
in achieving this transmission using the same wiring used for
transmitting video.
Robbins (U.S. Pat. No. 4,509,211) discloses the only known method
for transmitting control signals from an infrared transmitter over
a transmission line that also is used to transmit video signals.
That method converts the infrared signals received in the area of a
television to electrical impulses, which, due to the nature of
typical infrared control signals, are concentrated at frequencies
below 1 Mhz, lower than typical video frequencies. Those impulses
are transmitted across the transmission line to the area of a
programmable video source, where they are converted back to
infrared energy, recreating the original light pattern.
The technology taught by Robbins, however, is not adequate for
situations where the energy of other signals sharing the
transmission line is concentrated at frequencies that fall within
the frequency bands that confine the control signal energy. This is
the case when active telephone wiring serves as the transmission
line. Under the method Robbins discloses signals from infrared
controllers will conflict with telephone communication signals
because they both have information content at frequencies between 0
and 3 khz. Any receiver that is tuned to frequencies between 0 and
approximately 3 khz such as a telephone set, will react to both
telephone signals and control signals. Either telephone
communications will be noisy or the infrared signals will be
ambiguous or both. (If one signal is much stronger than the other,
that signal may be received without distortion.) Furthermore, the
system will fail whether or not video signals are present.
Robbins discloses devices that include in combination with other
technology. "isolation circuitry" which prevents the electrical
signals derived from infrared light patterns from reaching the
video source and the television receiver. Robbins teaches that
"power lines, telephone lines or other existing conductor systems
can be used, providing the various signals do not interfere, or
providing isolation means are provided." This is incorrect. If two
signals overlap in frequency no isolation means will cleanly
separate them so that only the desired signal reaches the receiver
that is designed to react to it.
Indeed, the isolation circuitry disclosed is totally unnecessary
even for the very application that is the focus of the Robbins
patent. Under the system Robbins discloses video signals and
control signals transmit across a single conductive path at
nonoverlapping frequencies and isolation circuitry is provided to
block the control signals from the video source and the television
receiver connected to this path. Because VCRs and virtually all
other video sources have reverse isolation provided at their output
ports, electrical energy incident at these ports will have no
effect at all, and extra isolation is not required. Further, when a
television is tuned to a particular video channel signals at
frequencies outside of that channel are ignored unless their energy
level is very high. The control signals will be ignored in this
manner, just as video signals at VHF channel 3 and VHF channel 5
are ignored by a television receiver tuned to VHF channel 4.
Beyond Robbins' incorrect teaching of isolation circuitry and the
fact that the infrared transmission system he teaches is inadequate
for the present application, Robbins teaches nothing regarding
transmission of video over telephone wiring.
An electronic transmitter/receiver pair called the Rabbit follows
the electronic principles disclosed in Robbins patent to send video
and infrared signals between a VCR and television. This device,
which cites the Robbins patent on its packaging has been available
at retail outlets since 1985. It uses a transmission line composed
of a single very thin insulated wire pair which must be installed
by the user between the VCR and a television. Thus. it embodies the
very difficulty that the current invention seeks to address.
There is another system known for transmitting infrared signals
from a television to a remotely located VCR, but it differs in that
it uses broadcast technology rather than a transmission line.
Called the "Remote Extender" and marketed by WindMaster
Manufacturing of DeFuniak Springs, Fla. this device converts the
infrared signals to electrical impulses then boosts these impulses
to a UHF frequency and feeds them to an antenna from which they
broadcast. A remotely located receiver picks up these UHF signals,
downshifts them back to their original frequency band and uses the
resulting impulses to recreate the original infrared pattern.
Because this system uses broadcast technology it is much more
susceptible to interference, and its receiver has the potential of
mistakenly picking up control signals from the transmitter of a
second transmit/receive pair operating nearby. Furthermore, it is
obviously more economical to use the telephone wiring for
transmitting control signals when combining with technology that
transmits video using that medium.
The simultaneous transmission of infrared control signals and a
single video signal across telephone wiring is the major focus of
the technology disclosed herein. It is easy to see, however, the
usefulness of extending this technology to allow signals from more
than one video source to transmit at a given time.
When each source transmits a signal at a different frequency band
the telephone wire medium should present no barrier to the use by
multiple sources. Many factors, however, limit the number of bands
that are available. An especially restrictive limit, of course, is
imposed by the difficulties of using telephone wiring as a medium.
In the event that the number of desired sources exceeds the number
of available channels, this limit becomes restrictive.
If a viewer can disable all but one of multiple sources that use
the same band, however, the picture from the remaining source can
be displayed without interference. This possibility creates a
demand for a technique that allows a user to quickly, conveniently,
and remotely activate one of several sources that are connected and
ready to transmit.
SUMMARY OF THE INVENTION
In view of the foregoing one object of the present invention is to
overcome the difficulties of transmission of video signals and
control signals from infrared transmitters across active networks
of telephone wiring.
In accordance with this and other objects, the present invention
includes a pair of transceivers: a first transceiver which is
designed for connection between a video source and a &telephone
jack or other port of access to a network of telephone wiring, and
a cooperating transceiver which is designed for connection between
an ordinary television receiver and a telephone jack. These
transceivers take advantage of the simple two-wire conductive paths
provided by the wiring of ordinary residential telephone systems,
and thus provide the following results, in stark contrast to known
techniques discussed above:
(1) Each television that is connected via a transceiver can
display, in addition to any of the other signals otherwise
available to it the signal from any video source connected via a
cooperating transceiver as described above.
(2) An unlimited number of televisions can connect and operate
simultaneously. Each television can select any of the connected
sources for display at any time, as long as the source is active.
i.e. conducting its signals onto the telephone network wiring.
(3) The number of sources that can be active at once will depend on
many different factors, but will always be greater than one. The
signals from each active source occupy different, nonoverlapping
frequency bands while transmitting across the wiring.
(4) Any number of sources can share a single frequency band, but
only one of that group can be active at a given time. The
transceivers that connect to the video sources will include one of
two technologies for allowing a viewer at any television to
remotely and conveniently switch the identity of the active source
that is using a particular band.
(5) Any video sources that respond to control signals from infrared
transmitters and are connected via a transceiver as described above
can be controlled from any area where a connected television is
located whether or not such area is within a line of sight of the
video source.
(6) Operation of telephone and other low-frequency communication,
including that conducted by intercoms, fax machines, and modems is
not affected by the connection and operation of any of the devices
herein described.
(7) All of the capabilities described above are provided by simple
connection of the transceivers. No other effort on the part of the
user is required.
In addition to these and other objects and results a design is
disclosed for a special television that connects directly to a
telephone network. This television is designed to cooperate with
the video source transceiver mentioned above. It includes
electronics for deriving video signals from the wiring and tuning
to them, and will transmit the intelligence of infrared control
signals that it detects back over the wiring to the transceiver for
control of its connected video source. Like the transceivers, it
causes no interference with telephone communications.
A further design is disclosed for an inexpensive device that in
combination with the disclosed transceivers and television,
provides the above capabilities to residences equipped with special
telephone systems that include a central electronic switching
unit.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram that illustrates the fundamental
components of the video source transceiver and how those components
interact with one another.
FIG. 2 is a block diagram that illustrates the fundamental
components of the transceiver that connects to a television and how
those components interact with one another.
FIG. 3 is a chart which describes the three systems disclosed for
cooperation betWeen RF conversion components of the two
transceivers.
FIG. 4 is a block diagram showing how special components can be
included within an ordinary television to provide for recovery of
video signals from active telephone networks and for transmission
of control signals onto those networks for reception by a
cooperating transceiver.
FIG. 5 shows the electronics of an adaptor designed to allow
transmission of RF energy across telephone networks that include a
central switching unit.
FIG. 6 shows the electronics used within the video source
transceiver for coupling to an active telephone network.
FIG. 7(shows the electronics used within the transceiver that
connects to a television for coupling to an active telephone
network.
FIG. 8 shows the details of the circuitry that converts infrared
light to electrical energy at frequencies above the telephone
voiceband.
FIG. 9 shows the details of the circuitry that creates an infrared
light pattern from an electrical signal above the telephone
voiceband.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The devices disclosed herein provide for transmission of video
signals and control signals from infrared transmitters across
active networks of telephone wiring without affecting ordinary
telephone communications. They are designed to accommodate video
signals with the same resolutions and refresh rates as those used
for public broadcasting. When transmitting signals across path
lengths typical of those found in ordinary residences the devices
provide enough signal fidelity to produce undergraded images and
unambiguous control commands.
Design of these devices required an extensive experimental and
theoretical investigation of the physics of transmission of video
signals across this type of network a deep appreciation of the
special need for convenience and economy in consumer products, some
circuit design as well as a novel combination of electrical signal
processing components.
A description of the disclosed devices is preceded by an overview
of the topic of transmission across telephone wiring. The overview
will begin with a summary of the investigation into the
transmission of video and will conclude with a description of the
method designed to transmit signals from infrared controllers.
The descriptions that follow the overview include several options
for the design of the pair of cooperating transceivers, the special
television/transceiver pair, and the special adaptor referenced in
the summary. The influence of the transmission investigation on
these designs as well as the influence of other considerations
related to consumer electronics will be included in those
descriptions. The advantages and disadvantages of the various
designs will also be discussed, and the perferred embodiment will
be identified. Finally the electronic details of some circuitry
described in general terms earlier on will be presented.
The signals described as video herein refer to signals that provide
picture information encoded according to NTSC, PAL, SECAM, or
similar formats that are used for public broadcasting throughout
the world. These formats provide between 50 and 60 image frames per
second, and vertical resolutions of between 525 and 625 lines per
frame.
In general, the disclosed devices are designed to transmit audio
information along with video according to these formats. Most of
the disclosed technology, however, will function the same whether
audio is present or not. For this reason, signals described as
video shall refer to signals with or without audio information. An
explicit description will be used whenever audio is specifically
included or excluded.
Transmission of Video Signals across Telephone Wiring
The following problems must be overcome for transmission of video
signals to succeed across a network of telephone wiring:
(1) Multi-path effects, also known as "reflections" or "ghosting,"
can cause video distortion. These effects can arise in a network of
wiring because signals can travel from source to receiver via many
different paths. If signal energy arrives at the receiver across
two paths that differ in length the signal conducted across one
path will be offset in time relative to the signal traversing the
second path. This will cause the same image to appear at two
different points in the scanning cycle of the picture tube. This
can create the special distortion pattern called "ghosting" if the
offset difference is large enough. Multipath "ghosting" of
broadcast signals is commonly caused by large buildings that
reflect broadcast energy and create multiple paths of significantly
different lengths to nearby antennae.
(2) Reduction of signal energy across the transmission paths can
reduce the signal-to-noise ratio present at a television receiver
below that required to produce a high-quality picture. A
signal-to-noise ratio of 40 dB is marginally sufficient for
high-quality video. It follows that picture degradation will result
whenever signal energy at the receiver falls to within 40 dB of the
noise level on the wiring or the minimum noise floor of the
television receiver.
Three factors are principally responsible for attenuation of the
energy of the signal as it travels from source to receiver,
resulting in a lower energy at the end of any transmission path.
These factors are:
(a) Attenuation or dissipation of signal energy by the wiring.
Unlike coaxial cable, over which video signals travel with little
attenuation, telephone wiring dramatically attenuates high
frequency energy. This attenuation increases linearly with path
length, and also increases with frequency. At 90 Mhz for example,
typical telephone wiring attenuates energy at 14 dB per 100 feet
while at 175 Mhz, attenuation is approximately 25 dB per 100
feet.
(b) Network junctions where the wiring splits. These can cause
significant attenuation when they occur on one of the principal
paths carrying energy from source to receiver. When the alternative
path is very long, the energy splits, reducing the level on the
main transmission path by approximately 3.5 dB. As the alternate
path becomes shorter, attenuation will depend on whether or not the
branch is open, or "terminated." If the branch is unterminated,
attenuation will be less than this amount, and will be negligible
for very short branches. At higher frequencies, the 3.5 dB limit is
approached more quickly.
(c) Telephone devices that dissipate high frequency energy. A
significant number of these devices exhibit this property. If they
terminate short branches, as described above, they can drain energy
from a principal transmission path. Devices that have a strong
dissipative effect can reduce the energy beyond the ordinary 3.5 dB
splitting loss. As the length of these branches increases the
attenuation of the branch prevents the draining phenomenon, and the
ordinary 3.5 dB splitting loss becomes the dominating factor. At
higher frequencies the 3.5 dB limit is encountered at shorter path
lengths.
(3) The fact that attenuation increases with frequency can cause
the energy near the high end of a 6 Mhz video channel to attenuate
more than the energy at the lower end. This causes a "tilt" in the
signal power spectrum, which is a form of signal distortion that
can cause picture degradation if it is sufficiently pronounced.
(4) Interference from strong broadcast signals picked up by the
wiring acting as an antenna can cause severe distortion. The
ability of the wiring to receive broadcast energy increases with
frequency.
(5) Because telephone wiring unlike coaxial cable is not shielded
by a grounded metallic conductor, significant electromagnetic
radiation can be created when it conducts electrical energy at
radio frequencies. This can create legal problems as well as
interference to nearby televisions and other receivers tuned to
those frequencies. The level of radiation caused by a given signal
level increases with frequency. (In contrast to regulations
covering radiation no special legal problems are created in the
U.S. by the connection of radio frequency devices to the public
telephone network if those devices do not transmit energy below 6
Mhz. Restrictions are not required because the network wiring will
quickly attenuate such energy below any meaningful level.)
One possible strategy for addressing these problems is to recode
the video signal into a different waveform with equivalent
information before imparting its energy to the wiring. If, for
example, the bandwidth of the signal could be compressed without
losing information, the problems of tilt interference, and,
possibly, radiation would be reduced. Implementation of compression
or other recoding techniques, however, is extremely expensive, and
will probably not significantly alleviate all of these
problems.
Because some conventions for video encoding and modulation provide
signals with redundant information the bandwidth of a video signal
can sometimes be reduced by sharp filtering without significant
loss of information. Because the potential reduction would not be
large, however, this strategy is also unlikely to significantly
alleviate the problems described above.
A second method of waveform alteration is to amplify the higher
frequencies of the signal more than those at the low end. This is
called "pre-emphasis" and can compensate for "tilting" of the
signal. Apart from the fact that it only addresses one of the
potential problems, however, pre-emphasis is expensive and also
requires the inconvenience of adjusting the compensation level upon
installation in a new residence. This is because the attenuation
differential is a proportion of the overall attenuation which, in
turn, will vary from one residence to another.
Beyond rewiring a residence which defeats the purpose of the
invention, the only other elements of control that can be exercised
to help transmission succeed lie in the choice of the energy level
and frequency, and in electronics that can limit the effects of the
connected telephone devices. Most individuals skilled in the art,
however, expect that an amplified video signal conducted across
telephone networks would suffer from "ghosting" at most any
frequency and energy level. Others suspect that amplification of
the signal high enough to force it across the wiring would create
completely unacceptable levels of radiation.
To investigate transmission over this network, the inventors
devised and conducted a series of experiments that included
observation of the quality of pictures generated from transmitted
signals, and also measurements of radiation created by the
transmitting signals.
As part of the experiment, a transmit/receive pair was designed,
using technology disclosed later herein to feed amplified video
signals through one port on a network and to recover them from a
second port. These devices were used to perform experiments in
twenty residences using video signals at different energy levels
and frequencies. For most of the experiments, telephone equipment
was disconnected at the involved ports, but some remained elsewhere
on the network. A few tests were performed to investigate the
effects of telephone equipment sharing the same port.
The radiation tests involved conduction of video signals on to an
unterminated 50 foot length of wiring that was extended
horizontally and elevated one foot above ground, and measuring
field strength via a calibrated antenna placed 3 meters from the
midpoint of the wire. The signals were conditioned to minimize
radiation before they were fed to wiring. The conditioning involved
a process called "balancing" which is used in the disclosed
transceivers and is described later on.
The most natural choices for transmission frequencies are the
channels in the low VHF range. In the U.S.. the low VHF range is
composed of VHF channels 2 through 6. which extend from 54 Mhz to
88 Mhz. VHF channels 2 through 4 constitute one adjacent group of
three 6 Mhz wide channels spanning between 54 Mhz and 72 Mhz, and
VHF channels 5 and 6 constitute a second adjacent group spanning
from 76 Mhz to 88 Mhz.
Channels in the low VHF range are good candidates for transmission
frequencies because they constitute the lowest group of channels
tunable by ordinary televisions. The benefit of tunability is that
television receivers can recover these signals from the wiring in
tunable form, eliminating the need for electronics that convert
their frequency. The benefits of using the lower frequencies among
the VHF channels are the attendant reductions in attenuation and
radiation.
A further advantage of tunability is that if the channel is not
used for local video broadcasting, there is no possibility of
interference from broadcast energy picked up by the wiring in the
U.S. That is because the frequency bands allocated to video
broadcasting in the U.S. are off limits to any other services.
Because little variation was expected across the low VHF range,
tests were conducted only at VHF channel 3. No frequencies above
this range were tested because the first tunable channel above VHF
channel 6 is VHF 7 which, at 174 Mhz, would exhibit significantly
greater attenuation and radiation, and would have no redeeming
advantages over the low VHF channels.
To see if further reductions in attenuation and radiation would
offset the extra costs associated with using channels below the
tunable range, it was decided to investigate transmission at
frequencies below VHF channel 2. Because U.S. Federal
Communications Commission radiation limits are less restrictive
below 30 Mhz, it was decided to choose the channel spanning from 24
Mhz to 30 Mhz.
To the inventors knowledge, the only applications involving
transmission of video signals with high resolutions and refresh
rates at frequencies below the tunable range are those where extra
bandwidth is needed on a cable TV distribution network. This
requirement can arise when there is a need to send video signals
over cable from remote locations back to a central transmission
site. These frequencies are available for reverse transmission
because distribution systems do not ordinarily use frequencies
below VHF channel 2. They are not tunable by televisions and have
never to the inventors knowledge been used in any consumer video
device.
Following is a summary of the results of the transmission and
radiation experiments:
(1) When a VHF channel 3 signal with a conducted energy level of
37.5 dB re 1 mV was fed onto the wiring at the source end. visibly
undegraded pictures were generated from signals recovered at a
remote jack in 85% of the test cases. Radiation from signals at
this energy level were measured at approximately 200 uV/M at 3
meters.
(2) At an energy level of 42.5 dB re 1 mV. video signals concenz
trated between 24 Mhz and 30 Mhz succeeded in generating a visibly
undegraded picture in 100% of the test cases. Radiation levels were
approximately 200 uV/M at 3 meters. (This level was the same as the
level for VHF channel 3 because a higher conducted signal level was
used.)
(3) Ghosting was never observed at any frequency or energy
level.
(4) Interference from a broadcast video source distorted the
picture only when it was strong enough to create an undegraded
picture via antenna reception. Distant video sources caused no
interference. This type of interference, of course, applied only to
the tests at VHF channel 3 and not at the 24 Mhz to 30 Mhz
channel.
(5) Signals from CB radio transceivers, which operate with 5 watts
of power and span the range from 26.965 Mhz to 27.4 Mhz caused
interference with transmission across the 24-30 Mhz video channel
when a CB transmitter was within 50 feet of the telephone wiring.
Interference from other sources was not noticed, but is obviously
possible when a source transmitting at an interfering frequency is
close enough or transmits with enough power.
(6) The connection of telephone equipment at ports previously used
only by the transceivers occasionally degraded an otherwise high
quality picture.
(7) No distortion that was noticed could be traced to "tilting" of
the signal spectrum.
(8) Radiation from signals transmitting across the wiring at VHF
channel 3 often caused slight but significant interference to
nearby televisions tuned to a VHF 3 signal supplied by a different
video source. This occurred most often when a cable converter and
VCR both connected to a television receiver, and the television
tuned in a signal from the cable converter at VHF channel 3 while
the VCR supplied the VHF 3 signal that was transmitted across the
telephone wiring. This type of interference occurred on older
televisions that did not offer a shielded input port, and also on
more modern televisions that connected via a shielded coaxial cable
but allowed slight leakage from other available ports such as twin
lead ports. Note that this type of problem will not arise when
using VHF channels 5 or 6 for transmission across the wiring,
because video sources that supply signals at those channels are
very rare.
The survival of enough signal energy to generate, a quality picture
can be explained by simply considering the attenuation expected
over the longest paths typically encountered in residences. If one
assumes a minimum television receiver noise figure of 5 dB. a
receiver bandwidth of 6 Mhz, and a desired signal-to-noise ratio of
50 dB, one finds that the minimum signal level required at the
receiver is 770 uV into 75 ohms. The output level of a typical VCR
is approximately 2000 uV into the same impedance, well above the
minimum necessary to reliably provide a high quality picture. At 66
Mhz. attenuation of signals transmitted over telephone wiring is
approximately 30 dB over 250 feet. It follows that 30 dB of
amplification should ensure good signal quality over the longest
paths in typical households, except where splits in the wiring and
connected telephone equipment cause excessive attenuation.
The lack of "ghosting" can be explained by the fact that there is
usually a monotonic relationship between signal transit time and
attenuation. (The rare exceptions to this relationship can be
caused by a short path over which signals suffer extraordinary
attenuation due to the presence of many splits, or the presence of
telephone devices connected off short branches. Signals traversing
such a path might attenuate more than those traversing a longer
path that has a longer transit time.) Because of this monotonic
relationship secondary signals arriving at the receiver after
traversing long reflected paths will be usually be significantly
attenuated relative to signals that travel over the most direct
path from the transmitter. The "offset" in the picture that
produces "ghosting" is related to the difference in travel times.
To be visible, the offset must be at least as wide as the
resolution of the television. It can be shown that path length
differences that create offsets this large also have enough
difference in attenuation to place the energy level of the
reflected path at least 40 dB below that of the incident path which
is below the minimum SNR required for a quality picture, making the
reflected energy negligible and its interference invisible.
The results of the experiments verified that when two signals are
fed to telephone wiring at energy levels that will cause them to
generate the same amount of electromagnetic radiation a signal
transmitting at a channel below 54 Mhz has a significantly higher
probability of generating a high quality picture than a signal
cies, however, is more susceptible to interference from broadcast
sources and also requires somewhat more expensive electronics.
Transmission of Signals from Infrared Controllers across Telephone
Wiring
As described in the introduction, the second signal that will be
passed between the transceivers is the control signal from an
infrared transmitter operating in the area of a connected
television. Part of the disclosed transmission technique follows
the known strategy of transducing the light pattern created by
these signals into electrical energy and transmitting that energy
across the wiring in the opposite direction of the video signals to
be received by the transceiver connected to the video source. That
transceiver uses the electrical version of the signal to recreate
the original infrared light pattern for the purposes of controlling
the video source to which it connects.
The technique disclosed herein embodies an extension designed to
avoid interference with telephone signals. The extension calls for
the frequency of the electrical version of the control signals to
be converted to a higher band before transmission across the
wiring. This band will be high enough to eliminate interference
with telephone or low-frequency communication signals. After
recovery of this signal at the end of the transmission path, the
signal is converted back to its original band before being used to
recreate the original light pattern.
Maintaining the fidelity of the control signals across the wiring
presents less of a challenge than was posed by transmission of
video signals. Unevenness, or "tilting" in the signal spectrum is
not a problem because the bandwidth of the signal is small. An
analysis of the factors governing multi-path interference indicates
that problem should not arise either.
Because the bandwidth of control signals from typical infrared
transmitters is considerably less than 1 Mhz finding a frequency
interval that will encounter little interference from ambient
broadcast signals is not difficult. Also, the information content
is small so that little energy is required for successful
transmission. The reduced energy generates less radiation.
Other requirements for the choice of a frequency band and energy
level for transmission of these signals are that the band must not
overlap, of course, the video signals at the frequencies chosen for
video transmission, and the energy must meet the legal requirements
that govern devices that connect to the public telephone network.
As mentioned earlier, the U.S. Federal Communications Commission
imposes no restrictions on signals above 6 Mhz. leaving ample room
between that frequency and the video signals. even if a channel
below VHF 2 is used. The control signals can also be transmitted
above the frequencies used for transmission of video.
A frequency centered at 10.7 Mhz is used in the preferred
embodiment because that is a common intermediate frequency in FM
radio devices, the result of which is that there are very
inexpensive electronic components available that are especially
suited for that frequency.
Description of the Transceiver that Connects to a Video Source
As a result of the investigation into transmission of video signals
across active telephone wiring and the system adopted for
transmission of control signals, a general design for a transceiver
was developed to connect between a video source and telephone
wiring to perform the functions of;
(1) shifting the frequency of the video signal from the channel
supplied by the source to the channel used for transmission,
(2) amplifying the video signal
(3) "balancing" the two leads of the video signal so that their
voltages are nearly equal and opposite with respect to ground, and
matching the impedance of the telephone wiring.
(4) transmitting this signal on to the telephone network without
disturbing low frequency communication signals, simultaneously
recovering the control signals fed to the wiring by the transceiver
connected to the television.
(5) downshifting the control signals to their original
frequency,
(6) using the resulting energy to recreate the original infrared
pattern, and
(7) connecting to a telephone jack while allowing for telephone
devices to share the same jack without loading down the energy of
the video signal.
FIG. 1 shows an arrangement of electronics for a transceiver 1
designed to implement these functions. This transceiver is
described in the following paragraphs. The description discloses
several optional design variations.
The transceiver 1 connects to the video source 2 to derive a
signal. That signal is passed to RF converter 3, which translates
the signal to the frequency band chosen for transmission over the
wiring.
Fortunately, nearly all consumer video sources provide their
signals in one of only two different ways. Some devices provide an
unmodulated video signal containing no sound information from one
port and an unmodulated audio signal from a second, separate port.
Others supply a video signal, possibly including sound information,
at either VHF channel 3 or 4, according to a switch set by the
consumer. Most VCRs make their signal available in both forms.
Two alternative design options for RF converters are disclosed for
transmission at a low VHF channel. These options have clear
advantages over all other possible designs. One design derives the
signals from the port that supplies a low VHF signal, hereinafter
referred to as the "low VHF port." That design is described first.
That description is followed by a description of the second design
which derives its signal from the port that supplies an unmodulated
signal, hereinafter referred to as the "baseband" port.
Operating manuals for video sources that provide a VHF channel 3 or
4 signal instruct users to select the channel not used for local
broadcasting. One of the two is always guaranteed to be free from
broadcast interference in the U.S. This is because the U.S. FCC has
allocated frequencies to ensure that no locality has broadcasting
at both of two adjacent video channels and has reserved the video
broadcast bands strictly for television.
It follows that the low VHF port on a VCR is guaranteed to provide
a low VHF signal that is not used for local broadcasting. This
eliminates the need for RF conversion electronics and significantly
reduces the expense of the device. Furthermore, a single design can
suffice for every location in the country.
A possible drawback to this alternative is that of the interference
problem, described earlier, caused by radiation of the transmitted
signal from the wiring that leaks into televisions deriving signals
from a separate source at VHF channel 3 or 4. To minimize radiation
and thus alleviate this problem, the use of a special connecting
cable and a variable amplifier are disclosed later on in the
description of this transceiver.
The second design option for transmission at a low VHF channel
calls for the signal to be derived in unmodulated form from the
baseband port. This option has two significant advantages. One is
that the low VHF port on VCRs is usually connected to a television
receiver, while the baseband port on VCRs is almost always unused
and open, making connection of the transceiver extremely easy.
The other advantage derives from a switch, usually referred to as
the "TV/VCR" switch that controls the output of the low VHF port on
VCRs. The TV/VCR switch allows the VCR signal created from a video
tape or from a signal tuned in by the VCR tuner, to be sent out at
VHF channel 3 or 4, or alternatively it allows the signals input to
the VCR to pass out the "low VHF" port at their original
frequencies. Meanwhile, the VCR signal always exits the baseband
port. This allows the local television to tune to either the input
signals, or to the signal produced by the VCR, while the VCR signal
exits the baseband port separately available for transmission
across the wiring to the remote television. Moreover, the "TV/VCR"
switch usually responds to one of the controls on an accompanying
infrared remote control transmitter.
If a low VHF frequency is chosen for transmission and the baseband
port is chosen as the signal source, the RF converter 3 is
obviously required. The converter inputs a video signal, and uses
that signal to modulate a low VHF carrier signal creating an
equivalent video signal at a low VHF frequency. (If an audio signal
is available it would ordinarily make sense, of course, for the
modulator to combine this signal together with the video according
to the NTSC or an equivalent format, and then use the combined
signal to modulate the carrier.) In order to achieve the economy
provided by a single design that suffices for the entire U.S.. one
of two adjacent low VHF channels should be made available and set
according to a user-controlled switch. (Theoretically, the switch
could also be automatically controlled using circuitry that detects
the presence of broadcast energy to choose the empty channel.) A
design for this modulator is not given because several designs are
well known.
Several advantages accrue if the modulator is designed to operate
at either VHF channel 5 or 6. instead of the other two available
adjacent low VHF pairs: VHF 2/3. and VHF 2/3. First of all, the
special problem of radiative energy from the wiring interfering
with the signal provided by a separate video source to a nearby
television will not occur. This is because consumer video sources
seldom provide their video signal at VHF channel 5 or 6. Secondly,
the television connected via the transceiver will more easily be
able to combine the recovered signal together with a local video
source, such as a cable converter, again because video sources
almost always use VHF channels 2, 3, or 4. Finally, an advantage
accrues from the fact that VHF channels 5 and 6 are not adjacent to
any other channels. This means that when combining the telephone
line signal with a signal from an antenna, the signal from the
telephone line will never be adjacent to more than one broadcast
signal. Because only expensive modulators confine their signals
completely within their intended band, this reduces possibilities
of interference.
The RF converter 3 is also required, of course, if a frequency
below VHF channel 2 is used for transmission, independent of the
port from which the video signal is derived. Unlike low VHF
channels, however, channels below VHF 2 are not tunable by ordinary
televisions, making RF conversion a requirement at the transceiver
that connects to the television, shown later in FIG. 2. The RF
conversions performed by the two transceivers must obviously
coordinate in this case. Three systems for coordination between
these conversion operations are disclosed following the description
of the television transceiver.
After it is derived at or shifted to the channel used for
transmission, the video signal is passed to an RF amplifier 4,
which increases the energy level by a fixed factor. In order to
increase the likelihood of success of transmission across all
residences, amplification should be set to cause radiation that
barely meets legal limits, unless a very high success rate can be
achieved with a lesser setting.
A variation of this design calls for an RF amplifier 4 that allows
the user variable control over the amplification level. This is
valuable in situations where VHF 3 or 4 is used for transmission,
because radiation from the wiring can cause interference at
televisions connected to separate sources, as described earlier. A
variable reduction of signal level potentially enables a user to
eliminate this interference while keeping signal level at the
remote television high enough to generate an undegraded
picture.
After amplification, the video signal follows the conductive path
to a coupling network 5. This network 5 feeds the video signal to
the telephone wiring, and allows the control signals from the
television transceiver to pass from the wiring towards the control
signal processing circuitry 6. (The process whereby control signals
from an infrared transmitter are converted to electrical energy
above voiceband and conducted on to the telephone line is included
within the description of the television transceiver.) The network
also performs the functions of balancing the energy of the video
signal, matching the impedance of the video signal path to the
impedance of the telephone wiring, blocking low-frequency telephone
communication signals from the transceiver electronics, and
blocking the flow of video signals towards the control signal
processing circuitry 6. The network 5 does not block the flow of
control signals towards the RF amplifier 4.
The importance of these functions is described in the following
paragraphs. The detailed electronic design of the preferred
embodiment of this network is shown in FIG. 6 and is described in
detail later on.
Balancing the video signal energy on the two leads of the wiring
promotes cancellation of the two electromagnetic fields created by
these leads, dramatically reducing radiation. The frequency of the
input will have the biggest effect on the balance achieved by a
given network design. Because the frequency will be known, the
design can be tailored to produce a reliable balancing.
Balancing of the control signals, on the other hand, is not nearly
as critical because the strength of those signals can be boosted
high enough to guarantee quality transmission while limiting
radiation to levels below legal or otherwise significant
limits.
The impedance of the internal transceiver circuitry wiring is
matched to the impedance of the telephone line at the video
frequencies because transition from one medium to another is
inefficient and wastes signal energy if impedance is not matched.
This can be important in situations where the video signal energy
is only marginally high enough to create a high quality picture.
Impedance matching at the frequencies used by control signals is
not important because of the excess power available for
transmission of those signals.
Blocking low-frequency signals from transmission to the electronics
of the transceiver prevents any interference with ordinary
telephone communication signals. The blocking should render the
connection and operation of the transceiver totally transparent to
the functioning of low frequency telephone communications.
Blocking the flow of video energy to the control signal processing
circuitry 6 allows that component to reliably recreate the original
control signal without special expensive electronics. The video
signal would ordinarily disrupt this processing because it has a
very high energy level while passing through this network.
Note that the network 5 allows control signals to pass on to the RF
amplifier 4. There is no need to block these signals because they
will be at frequencies above baseband and RF amplifiers are
commonly designed to terminate low power RF signals that are
incident at their outputs. The amplifier thus provides isolation of
the control signal from the video source as a side effect. If this
intelligence could traverse the amplifier and transmit to the RF
converter 3 or the video source 2, it would be similarly ignored,
because these devices also commonly provide reverse isolation.
The function of the control signal processing circuitry 6 is to
downshift the frequency of the control signals back to their
original location at baseband, and to use the resulting energy to
drive an infrared emitting bulb 7, recreating the original light
pattern. This function completes the process of transmission of
signals from an infrared transmitter over active telephone wiring.
a function not heretofore a part of any commercial or consumer
device. The preferred embodiment of the control signal circuitry 6
of the video source transceiver is shown in FIG. 9 and is described
in detail later on.
If the video source transceiver is placed on top of the source to
which it connects, which seems likely to be the most convenient
placement, there will not be a line of sight path between the
infrared bulb and the infrared sensitive pick up window on the
source. This is not a problem if the infrared light can reflect off
walls and retain its effectiveness, something that is known to be
possible. To allow this convenient placement of the transmitter,
the infrared transmission bulb should be driven at high power and
with a wide beamwidth, in order to decrease the possibility of
insufficient reflective energy. It may make sense to drive several
bulbs oriented at different angles.
The transceiver 1 connects to the telephone network 10 via a
connecting cord 12 terminated with a male RJ-11 plug, the standard
plug used to connect to telephone jacks. This cord includes two
special components, a touch tone switch 8, and a low pass filter 9.
Also, the two conductors of the cord are systematically twisted
about each other.
The touch tone switch 8 is an optional feature provided for
coordination of this transceiver with other video source
transceivers connected to the same network. Its function is
described in detail later on. For the purposes of the current
discussion. it can be assumed that the switch has no influence on
signal flow across the cord 12 or on the operation of the other
components. The other two features, the low pass filter 9 and the
special nature of the conductors of the cord, are described in the
following paragraphs.
As mentioned earlier, telephone devices that connect to a main
transmission path via a short stretch of wiring can cause
significant dissipation of RF signal energy. To allow equipment to
remain connected at the ports shared by the transceiver without
causing attenuation, the low-pass filter 9, consisting of two
induction coils with low-pass properties, connects in series to the
two conductors of the cord to offer a second port for connection of
telephone equipment 11. This filter removes most high-frequency
effects of both the equipment and the split in the wiring by
presenting a high impedance to RF signals.
Twisting the conductors of the cord significantly reduces the
energy that radiates from those conductors, beyond the reduction
that derives from balancing the voltages. When used in combination
with the low-pass filter, this feature leaves only the wiring
connecting the jacks to the public telephone interface, and the
wiring connecting telephone devices at uninvolved jacks as a source
for significant radiation. (If the connecting wires are twisted.
and uninvolved jacks are far from the main transmission path, very
few radiation opportunities will remain.) This reduction is
important for the case where a television receiving a signal from a
separate video source encounters interference from radiation
generated by the wiring at VHF channel 3 or 4.
Shielding of the conductors by a metallic conductor also will
reduce radiation. This shielding is more effective if the conductor
is connected to ground.
Description of the Transceiver that Connects to a Television
Receiver
Based on the system adopted for transmitting infrared signals. and
the requirements for conveniently supplying video signals to a
television receiver, a general design for a transceiver was
developed to connect between telephone wiring and a television
receiver to perform the functions of:
(1) receiving ambient infrared control signals, converting them to
electrical energy, and boosting the frequency of this energy to a
band that lies completely above the frequencies used for ordinary
telephone communications.
(2) feeding the control signal on to the telephone network without
disturbing low-frequency communication signals, while
simultaneously recovering video signals.
(3) matching the impedance between the telephone wiring and the
conductive path that receives the video signal,
(4) converting, if necessary, the received video signal up to a
channel that is tunable by a television and is not used for local
broadcasting, and
(5) connecting to a telephone jack while allowing for telephone
devices to share the same jack without loading down the energy of
video signals on the wiring.
FIG. 2 shows an arrangement of electronics for a transceiver 15
designed to implement these functions. This transceiver 15 is
described in the following paragraphs. The description discloses
several optional design variations.
An infrared sensitive diode 16 reacts to control signals from an
infrared control signal transmitter 23 to create the desired
conversion to electrical energy. The resulting signal is passed to
the control signal processing circuitry 17 which performs the
translation to a frequency band above the telephone communications
band. The preferred embodiment of this circuitry is shown in FIG. 8
and described in detail later on. The preferred embodiment calls
for a transmission frequency centered at 10.7 Mhz.
Signals generated by the control signal processing circuitry 17 are
passed to a coupling network 18. This network feeds the control
signals to the telephone network wiring 26 and allows video signals
to pass from the wiring along the conductive path leading towards
the television receiver 22. The network also performs the functions
of matching the impedance of the video signal path to that of the
telephone wiring, blocking low-frequency signals from the
transceiver electronics blocking the diversion of video energy
towards the control signal processing circuitry 17, and blocking
higher harmonics of the control signal, but not the fundamental of
this signal from transmission to the telephone wiring and from
transmission along the conductive path leading towards the
television 22.
The importance of these functions is described in the following
paragraphs. The detailed electronic design of the preferred
embodiment of this network is shown in FIG. 7 and is described in
detail later on.
Impedance matching ensures an efficient transfer of energy from the
telephone wiring to the electronics of the device. Just as in the
case of the video source transceiver, the efficient transfer of
video energy across this junction can be important in situations
where the signal energy is only marginally sufficient to produce a
high quality picture.
Blocking telephone and other low-frequency communications signals
from transmission to the electronics of the transceiver prevents
any interference with those signals and also prevents disturbance
of the DC power supplied to telephone devices. The blocking should
be such that it renders the functioning of these communications
totally transparent to the connection and operation of the
transceiver.
Blocking of video signal energy from transmission between the
network 18 and the control signal processing circuitry 17 is
important because it prevents the reduction of video signal energy
by diversion along this path.
Blocking the harmonics, but not the fundamental, of the signal
emerging from the control signal processing circuitry 17 is
important because some of the harmonics may coincide with the
frequencies used for transmission of video. Because they will
transmit to the television 22 as well as to the telephone wiring
these harmonics can cause interference if they are of sufficient
strength. No information is lost in this process because the
information in the harmonics of a signal is completely redundant
with the information in the signal fundamental.
Unless the energy level of the control signal is very high, there
is no need to block the control signal from transmission across the
network 18 towards the television receiver 22. This is because
television receivers ignore energy outside the video channel to
which they are tuned unless that energy is at a very high level.
For example, televisions ignore energy at VHF channel 4 when they
are tuned to VHF channel 5. Problems also do not occur when the RF
converter 19 is required. In that event, the control signal is
shifted in frequency along with the video signal, but it is
rejected by the television tuner for the same reasons as before.
Because the control signal cannot cause interference or other harm
to the television transceiver, the isolation circuitry described by
the Robbins patent, which blocks this intelligence from the
television, is unnecessary.
Signals passing along the path from the network towards the
television 22 encounter the RF converter 19. As mentioned earlier.
if a low VHF channel is used for transmission, frequency conversion
at the television end is not necessary and signals can transmit
directly from the coupling network 18 to the television 22.
When channels below VHF 2 are used for transmission, the RF
converter 19 converts the video signal to a channel that is tunable
by ordinary televisions. Because of potential interference
problems, this channel should be one that is not used by local
broadcasting. (Interference could normally be avoided by connecting
the transceiver via a shielded coaxial cable. Many older
televisions, however, do not offer a shielded input port, and many
modern televisions exhibit slight leakage from other available
ports such as twin lead ports.)
Because the video source transceiver outputs video signals at the
transmission frequency, and this transceiver 15, inputs signals at
that frequency, the two units must obviously cooperate in their RF
conversion designs. Three systems are disclosed herein for
cooperation between the RF converters of the disclosed transceiver
pair to transmit video at a channel below VHF 2. Under each of
these systems, the signal is provided to the television 22 at one
of two adjacent broadcast channels, according to a switch set by
the user. In the U.S., this feature guarantees that the requirement
of providing a signal at a channel not used for local broadcasting
is fulfilled because, as described earlier, the U.S. FCC has
ensured that one of two adjacent channels is always unused in a
given locality. A complete description of each of these systems is
presented in the next section.
The television transceiver connects to the telephone wiring network
26 via a cord terminated with a male RJ-11 plug. Just like the cord
used for connection of the video source transceiver, this cord
contains a low pass filter 24, which creates an isolated port that
allows connection of telephone equipment 25 without loading down
the video signal passing from the network to the transceiver.
Unlike the cord connecting the video source transceiver to the
telephone wiring, it is not as critical to supply this transceiver
with a cord whose conductors are twisted. That is because the level
of the video energy traversing the cord will be much lower, and
will generate less radiation.
Because the television to which this transceiver connects may have
another source of video signals available, and because most
televisions only have one port for input of signals at VHF
frequencies, it may make sense to provide a switch that allows
users to connect both sources and quickly choose between them.
Because of the likelihood that no signals from the two sources
contain energy at the same channel, any device or component that
performs this function might also allow the addition of the two.
Technology to achieve these signal combination options is well
known.
Such a component, not shown in the drawings, could be an attachment
that connected in series with the cable connecting to the
television. It might be more convenient, however, to include this
component as part of the transceiver. In that case, the transceiver
would simply include a coaxial port for input of signals from a
second source, and would be able to provide signals from either
source, or the combination of the two, to the local television.
Controls on the transceiver would allow the user to choose the
composition of the signal provided to the television.
There is a possibility that, when receiving signals from a video
source located relatively close by, this transceiver 15 may receive
a signal whose energy level is too high for the television to which
it is connected. In the event that the transceiver includes RF
conversion circuitry the solution is to ensure that this circuitry
can manage high signal levels, and that a level within the range of
most television receivers is provided at the output. When a low VHF
channel is used for transmission and RF conversion circuitry is not
required, one solution is to provide attenuation circuitry, set
automatically or manually, that reduces the energy of the signal to
a level within the dynamic range of ordinary televisions.
Systems for RF Conversion to Achieve Transmission below VHF Channel
2
As mentioned earlier, two RF conversion operations are required in
order to transmit the video signal across the wiring at a channel
below VHF 2. At the video source end, the transceiver must convert
the signal from the frequency at which it is supplied to a band
between 6 Mhz and 54 Mhz. The transceiver connected to the
television must recover the signal from within this band and
convert it to a channel tunable by ordinary television receivers.
Three systems for cooperation between these conversion operations
are described in the following paragraphs, along with their
respective advantages and disadvantages.
Under each of the systems, the signal is provided to the television
22 at one of two adjacent broadcast channels, according to a switch
set by the user. In the U.S.. this feature guarantees that the
requirement of providing a signal at a channel not used for local
broadcasting is fulfilled because, as described earlier, the U.S.
FCC has ensured that one of two adjacent channels is always unused
in a given locality.
The unusual nature of the conversion operations, combined with the
novelty of using these channels for a consumer video application,
or for any video application other than the cable distribution
function described earlier, make the resulting electronics a new
consumer electronic development.
The systems are summarized by the chart in FIG. 3. The precise
electronic details of the various converters are not given because
technology to achieve these conversions is known, and would be
within the ability of one of working skill in this field.
Under the first system, the video source transceiver derives its
signal from a low VHF port and imparts a fixed downshift to produce
one of two adjacent channels. Signals spanning 24 Mhz to 30 Mhz or
30 Mhz to 36 Mhz, for example are produced from VHF channels 3 or 4
by a fixed downshift of 36 Mhz. In the final step of this system,
the RF converter in the television transceiver imparts an
equivalent fixed upshift, restoring the signal to its original
channel for delivery to the television. The fixed downshifts mean
that the choice of which of the two channels is actually used for
transmission is determined by the setting on the video source that
chooses between VHF channel 3 or 4.
(There are a few video sources that supply signals at VHF channels
2 or 3 instead of VHF channels 3 or 4. To account for these
sources, the shifting should be designed to include bands covering
at least 18 Mhz. rather than 12 Mhz.)
The advantage of this system is that the versatility already
supplied by the low VHF port of the video source is used to ensure
that the transmitted signal is supplied to the television at an
unused channel. This enables the two RF converters to be designed
to translate by a fixed amount, reducing manufacturing costs.
The second system calls for the RF converter in the video source
transceiver to use the video signal from a baseband port to
modulate a carrier to either one of two adjacent channels below VHF
2. according to a switch set by the user. (It would ordinarily make
sense of course for the modulator to combine an audio signal, if
available, together with the video according to the NTSC or an
equivalent format, and then to modulate using this combined
signal.) In cooperation with this conversion, the RF converter of
the television transceiver again upconverts by a fixed amount. If
the modulation created the channels spanning either 24 Mhz to 30
Mhz or 30 Mhz to 36 Mhz. for example, an upshift of 36 Mhz would
produce VHF channels 3 or 4. an upshift of 52 Mhz would produce VHF
channels 5 or 6, and an upshift of 150 Mhz would produce VHF
channels 7 or 8.
The primary advantages of this design over the first are those
advantages, described earlier, that accrue to designs that derive
signals from the baseband port of the video source. There is also a
convenience in that inexpensive modulation ICs are available that
provide much of the circuitry necessary to build video modulators
with options for one of two carriers in the 10 Mhz to 100 Mhz
range. Finally, being able to choose adjacent VHF channel pairs
other than VHF channels 3 or 4 allows combination of the signal
passed to the television with signals from most common video
sources.
Two variations to the second system are now disclosed. In the first
variation, the switch will be automatically controlled. It will
rely on circuitry that samples the telephone line to detect the
presence of broadcast energy at either of the two channels used to
provide the signal to the television. (Broadcast energy will be on
the telephone line because it acts as an antenna to some extent.)
It will set the RF converter in the video source transceiver to
provide a transmission frequency so as to ensure that the channel
ultimately presented to the television receiver will be one unused
for local broadcast.
In the second variation, the RF converter in the video source
transceiver will simultaneously provide the video signal at both of
the two adjacent channels below VHF 2, so that when the television
transceiver converts the 12 Mhz band spanning these channels, it
produces signals at both of the two adjacent tunable channels.
The third system also calls for the video source transceiver to
derive its signal from the baseband port, but it includes an RF
converter that has only a single carrier which modulates the signal
to a single fixed channel that is used for transmission. The RF
converter in the television transceiver then performs either one of
two upward conversions, according to a switch set by the user.
resulting in one of two adjacent low VHF channels. If the
transmission channel spanned 24 Mhz to 30 Mhz, for example,
upshifts of 36 Mhz and 42 Mhz would produce VHF channels 3 and 4,
and upshifts of 52 Mhz and 58 Mhz would produce VHF channels 5 and
6.
In a variation of this strategy the RF conversion component of the
television transceiver allows continuously variable manual tuning,
in place of two fixed upshift conversions. This tuning must, of
course, allow the signal presented to the television to span two
consecutive channels. The provision of manual tuning reduces the
precision required for both converters resulting in a certain
economy.
Like the second design, the two variations of the third design also
enjoy the advantages of baseband input, and the advantage of being
able to output adjacent VHF frequencies other than VHF 3 and 4. The
main advantage over the second design is that the single optimal
sub-VHF 2 channel, in terms of radiation, attenuation interference
from broadcast sources, legal restrictions, and expense of
conversion electronics, can be chosen.
Because of these advantages, and because transmission over channels
below VHF 2 affords reliability which is of enormous importance in
consumer products, this third system is the preferred embodiment.
Furthermore, the fixed and not the variable tuning is preferred
because of the importance of convenience in consumer products. The
preferred channel spans from 24 to 30 Mhz because there is a
liberalization of U.S. FCC radiation restrictions below 30 Mhz, and
because the conversion electronics are slightly more expensive when
lower frequencies are used. Finally, it is preferred to present the
signal to the television at either VHF 5 or 6, because of the
advantages of combining those channels with broadcast signals or
other video sources. (These preferences may change as a result of
data not currently available to the inventors such as, specifically
but not exclusively, information regarding the frequency, strength,
and location of RF sources throughout the U.S. that may provide
interference at channels below VHF 2.)
Two further variations to the third system are now disclosed. In
the first of these, the switch will be automatically controlled. It
will rely on circuitry to detect the presence of broadcast energy,
to set the RF converter of television transceiver to convert the
transmitted video energy to the channel unused for local broadcast.
In the second variation, the RF converter of the television
transceiver will simultaneously provide the video signal at both of
the two adjacent tunable channels.
Description of the Special Television Receiver
The transceiver pair disclosed above provides an ability to view
and control a video source at a remotely located television. A
significant economy can be achieved, however, if the function of
the disclosed television transceiver is internalized in the
television electronics.
A special television 30, shown in Figure, provides such a
combination. This television is intended to cooperate with the
video source transceiver described above. It comes equipped with a
cord that includes a low pass filter 32, similar to those used with
the transceivers described earlier, for allowing telephone
equipment 33 to share the same jack without loading down video
signals on the wiring.
The television includes an IR sensitive diode 42, for converting
infrared signals into electrical signals. These signals are passed
to the special control signal processing circuitry 37 and the
standard control signal processing circuitry 41. The standard
circuitry 41 reacts to these signals to execute control over
television operations in the ordinary manner. The special control
signal processing circuitry 37 translates the electrical version of
the control signals to a frequency band above the highest frequency
used for ordinary telephone communications, and passes them to the
coupling network 34.
The functions performed by the special control signal processing
circuitry 37 are the same functions performed by the control signal
processing component included in the transceiver, described
earlier, that connects to the television. The preferred embodiment
of the circuitry is also the same. This embodiment is shown in FIG.
8 and is described later on.
The coupling network 34 allows the control signals to pass to the
telephone network wiring 31 and video signals to transmit from the
wiring along the conductive path leading towards the RF converter
35. The network 34 also performs the important functions of
matching the impedance of the conductive path leading to the RF
converter to the impedance of the telephone wiring, blocking
low-frequency signals from the television electronics, blocking the
flow of video signals towards the special control signal processing
circuitry 37, and blocking harmonics of the control signal, but not
the fundamental of this signal from the telephone line and the
conductive path leading towards the RF converter 35.
The functions performed by this network are the same functions
performed by the coupling network included in the television
transceiver described earlier. An explanation of the importance of
these functions was included in the description of that device. The
preferred embodiment of the network used here is also the same.
This embodiment is shown in FIG. 7 and described later on.
Both the video and RF control signals pass from the coupling
network 34 to the RF converter 35. That component will convert the
video signal to a channel that is tunable by ordinary television
tuning electronics. If a low VHF channel is used for transmission
across the wiring, however, ordinary television tuners can tune to
the transmitted signal and this component is not necessary.
Signals emerging from the RF converter 35 transmit to the RF signal
combiner 36. (If the RF converter 35 is not needed, signals flow
directly from the coupling network 34 to this combiner.) The RF
combiner 36 will accept video signals from a local video source 43
if one is available. It will add signals from the two sources, or
will choose the signals from one source or the other to pass along
to the tuning section 38. The final composition of the signals
passed to the tuning section 38 will be set by manual controls on
the television 30 or by infrared control signals received by the IR
sensitive diode 42.
The RF converter 35 disclosed herein can cooperate with the RF
converter of the video source transceiver using one of the three
alternative systems, described earlier, for cooperation between RF
conversion components at the two ends of the communication path.
The RF converter 35 included in the television will simply perform
the same functions as the RF converter of the television
transceiver described earlier, while the RF converter in the video
signal transceiver will perform the corresponding conversion.
A variation of the third system for cooperation between converters
is now disclosed for the case of the special television receiver
30. Under this variation, the RF converter 35 demodulates the video
signal it receives, and injects that signal into the television at
the point where it ordinarily expects demodulated signals. (The
demodulated signal will not go into the combiner in this case,
eliminating the need for that component. Signals from a local video
source 43 will pass to the tuner without combination.) This
variation liberates the converter from providing a signal at either
one of two adjacent channels, and might be less expensive, overall,
than the alternative.
Note that the RF converter 35 is not necessary if the television
tuner 38 can tune to signals below VHF channel 2. This converter is
offered as an alternative to providing the television with a
special tuner because it may be less expensive to adapt the design
of an ordinary television by adding this simple component.
In the preferred embodiment, the video signal transmits across the
wiring at a frequency below VHF channel 2, and the RF converter is
required because the television tuning section 38 tunes in only the
ordinarily tunable channels. A channel below VHF 2 is preferred
because of the decreased probability of picture degradation, and
the RF converter is preferred because the inventors believe that it
is less expensive to adapt the design of an ordinary television by
adding a converter.
A transmission channel spanning 24 Mhz to 30 Mhz is preferred, and
it is preferred that the RF converter of the television convert
that channel upwards by either 52 Mhz or 58 Mhz to VHF channels 5
or 6. according to a switch setting on the television, or a command
from the infrared controller. This embodiment follows the preferred
system, presented earlier, for coordination between the RF
converter of the video source transceiver and the RF converter of
the television transceiver. The justifications used earlier also
apply to this case. The option of demodulating the video signal is
not currently preferred because the expense of this option is not
clear.
Television 30 is novel in the following three respects. First, it
connects to active telephone networks, without causing
interference, to derive video signals, in addition to the video
signals it derives from other sources. Secondly, in addition to
detecting infrared signals for the purposes of controlling
television functions, it converts these signals to electrical RF
energy, and passes them on to the telephone line for controlling
the video source in cooperation with another device. Finally, it is
able to tune to signals at channels below VHF 2.
When the television 30 cooperates with the video source transceiver
1 described above, they allow the user to watch and control a video
source from a remote location. To further increase the usefulness
of this combination without significant extra cost, a unique
combination of this pair of devices with a special piece of known
technology is disclosed in the following two paragraphs.
To control the video source from the area wherein the special
television receiver 30 is located, the infrared transmitter unit
that controls that source must ordinarily be available at that
location. This is not always convenient, because this unit is
obviously often required at the location of the video source. If
the television 30 is provided with its own infrared controller,
inclusion of the command set of the video source controller as a
subset of the available commands significantly increases the
convenience of the system without significant extra cost.
Recently, infrared control units with large command sets that
include those of many different controllers have become available,
as have other units that have the ability to learn the command sets
from virtually any other controller. The novel combination
disclosed here adds a similar universal controller together with
the disclosed cooperating television 30 and transceiver 1. This
will significantly increase the usefulness of that pair of
devices.
Systems for Avoiding Interference from Broadcast Sources
The signals transmitted by the devices disclosed above travel from
source to receiver via conduction across telephone wiring. A
potential problem of this technique, described earlier, is that RF
broadcast energy from nearby sources can be received by the wiring
and interfere with the signal of interest. Under the design option
where the video signals transmit at a low VHF channel, the devices
provide signals at a channel unused by any local service. This
protection is not available when the video signals transmit at
frequencies below VHF channel 2. The following factors, however,
make the possibility of interference unlikely:
(a) The signal-to-noise ratio required for a quality video picture,
approximately 40 dB, is relatively low. Interfering signals must
have energy levels within 40 dB of the signal of interest to
visibly degrade a picture.
(b) The signal of interest is conducted directly on to the wiring.
The interfering signal must be received by the wiring acting as an
antenna, a much less efficient method of creating conductive
energy.
(c) The ability of the wiring to receive broadcast energy decreases
with decreasing frequency.
(d) The level of the signal of interest can be boosted to reduce
the potential of interference. (Because of legal and technological
constraints, however, there are limits to the level to which this
energy can be boosted.)
Despite these factors, tests have indicated that interference can
occur. Three methods for avoiding interference problems are
discussed below.
(a) One can choose a frequency band that is less likely to be used
by many transmitters operating at high power near residential
areas. This strategy requires a survey of frequency allocations and
broadcasting patterns. Preliminary investigation by the inventors
revealed that amateur radio is allocated narrow bands at 7 Mhz, 14
Mhz. 21 Mhz, and 28 Mhz, conveniently leaving gaps of 7 Mhz--just
right for video.
(b) The video source transceiver can simultaneously transmit its
signal over two frequency bands, and the signal that encounters
less interference can be chosen, at the television end, to provide
the picture.
In the case of the cooperating transceiver pair, the video source
transceiver simultaneously transmits the same signal over two
different and non-overlapping channels below VHF channel 2. The RF
converter of the transceiver that connects to the television
chooses, according to a manual control or an automatic process, to
accept one of the two channels, converting the energy within that
channel to a tunable frequency unused for local broadcast.
(Circuitry to automatically choose the less "noisy" channel would
have to include means to detect the presence of broadcast energy
within each of the two channels.)
In the case of the special television that cooperates with the
video source transceiver and includes a special RF converter, that
converter performs the same functions as the converter in the
television transceiver. Under the design option wherein the
television tuner can tune directly to signals below VHF channel 2
(and a converter is not involved) the tuner simply tunes to one
channel or another.
(c) Because the information at the edges of an NTSC video signal is
redundant, these edges can be filtered out before presentation to a
television, removing any interfering energy at those edges.
Specifically, the first 1.25 Mhz in an ordinary NTSC channel, known
as the vestigial side band, can be filtered out before presentation
to the television. This will reduce the video bandwidth from 5.75
Mhz to 4.5 Mhz, reducing opportunities for interference. In the
event that research shows that this causes some degradation of
picture quality, the vestigial side band can be recreated free from
interference within the shielded television transceiver, using
known techniques.
The upper 0.25 Mhz of the full 5.75 Mhz video signal can also be
filtered without significant reduction in picture quality. Trimming
this energy, however, will remove the audio information, which is
located immediately above the video information. The solution is to
transmit the audio signal at a different frequency. converting that
signal to its proper place before presentation to the
television.
Systems for Simultaneous Transmission of a Second Video Signal
A video source transceiver connecting a second source to the same
residential wiring network obviously has to transmit its signal at
a different frequency in order to operate simultaneously with the
first source. Ideally, this transceiver cooperates with the
television transceiver unit without requiring any design changes to
that transceiver. That allows the most economical design for the
primary transceiver pair, and still allows expansion of the system
to include a second source.
If low VHF channels are used for transmission, design of the second
video source transceiver is straightforward. That transceiver
simply transmits its signal at one of a second pair of adjacent low
VHF channels. If, for example, the primary video source transceiver
uses VHF channel 5 or 6, the secondary transceiver could use VHF
channel 2 or 3. The television transceiver described earlier will
supply both signals to the television receiver without any design
changes.
If the primary transmitter uses a channel below VHF 2, and the
secondary transceiver uses a low VHF channel, a slight alteration
in the design of the transceiver that connects to the television is
required. The alteration calls for an extra signal path to the
television that bypasses the RF converter. That path includes the
unshifted low VHF signals which could be easily combined with the
signal that was converted up by the RF converter. The channel
generated by the RF converter, of course, will have to be different
from the channel used for transmission of the second source.
Things are more complicated when both video signals transmit at
channels below VHF 2 because the television transceiver must
convert a second signal to a second tunable channel that is not
used for local broadcasting. The shift in frequency required by the
second signal, moreover, may not necessarily be the same as that
required by the first signal. The largest problem, however, may be
finding an extra 6 Mhz that is free from broadcast source
interference.
Extra transceivers that transmit video over the same channel as the
primary transceiver can be connected, of course, as long as a
viewer can disable all but one of the resulting group of connected
transceivers. In the following paragraphs, two designs are
disclosed for systems that allows a user to quickly, conveniently,
and remotely activate exactly one of several connected video source
transceivers transmitting at the same frequency.
The first design calls for the signal from all but one of the
transceivers to be blocked from transmission on to the wiring. The
blocking is accomplished by the touch tone switch 8 shown in FIG.
1. This switch connects on the cord between the transceiver and the
telephone jack, and contains a low pass filter, or other means that
completely block signals above a frequency that is below the
frequencies used for video transmission. It has two settings, one
of which enables the filter and the other which defeats it. The
switch reacts to the DTMF (dual tone multi frequency) touch tones
commonly created by telephones, allowing users to conveniently
select the active source from among the several connected. Any
logical command system will suffice. The electronic details of this
switch are not shown because RF filters and touch tone controls are
well known.
The second design calls for each of the video source transceivers
that transmit at the same frequency to derive its AC power via
powerline switches similar to those built by the X-10 Corporation.
These switches connect between power cords and AC outlets. They
detect high frequency control signals fed onto the wiring by a
remote device, and respond by blocking or enabling power to pass
along the power cord to the connected electrical device. This
allows one to remotely control the AC power to any device in a
residence via control signals sent through the AC wiring. Thus. a
user could conveniently select one of many sources sharing a
transmission frequency by activating the AC power for the
transceiver of that source and none of the others.
Because the first design uses ordinary touch tone telephones to the
send signals that establish the identity of the active transceiver,
it is preferred over the second design, which requires special
transmitters to send those signals.
Description of the Adaptor for Central Telephone Switching
Devices
As mentioned in the introduction, a reliable conductive path is not
always available in residences where each jack is wired directly to
a central electronic interface unit that connects to the public
telephone system. Because of the topology of these networks,
potential conductive paths from one jack to another will always
traverse this unit, where their continuity is likely to be
broken.
To allow the disclosed devices to operate on such a network, an
inexpensive adaptor 52 is disclosed. This adaptor is shown in FIG.
5.
Normally, the wiring leading from the jack 50 in the first area 51
would connect to the port 56 on the electronic switching unit 58
dedicated to the first area. Similarly, the wiring leading from the
jack 53 in the second area 54 would connect to the port 57 on the
unit dedicated to the second area.
The adaptor 58 reroutes these connections through a pair of low
pass filters 59 and 60. These block the transmission of high
frequency signals away from the switching unit, eliminating
attenuation. The filtering can be achieved by the same pair of
inductors disclosed earlier that achieve low pass filtering of any
telephone equipment that shares a jack with either of the two
cooperating transceivers.
The high pass filter 61 connects the paths leading from the first
area 51 to the second area 54 at high frequencies, completing the
conductive path for video and control signals between the
associated jacks. Transmission of low-frequency energy across this
path is blocked, maintaining separation of the telephone and other
low frequency communication between each jack and the switching
unit. In the preferred embodiment, the high pass filtering is
achieved by a pair of 100 pF capacitors, connected as shown.
The problem of inadequate video signal energy in the area where the
television is located was described earlier. Because the disclosed
adaptor offers access to the signal near the midpoint of its
transmission path, it offers a new solution to this problem. The
solution, not shown in the drawings, calls for an amplifier to
accompany the adaptor. A path leading from a video source could be
passed through this amplifier just before connection to the
adaptor. In this way, part of the total amplification required
could be imparted at the video source transceiver, and the other
part at the switching unit. This would reduce the peak signal power
at any point for a given level of total amplification, thus
reducing the maximum level of radiation.
For systems that also transmit control signals, a bypass around the
amplifier for transmission of these signals would have to be made.
The bypass would simply be a conductive path around the amplifier
including a filter to block video signals. Similarly, the input to
the amplifier would require a filter to block out control
signals.
Because the technology disclosed herein is not limited to
residential networks, and because "star" wiring configurations
including a central switching unit are very common among telephone
networks installed in commercial buildings, including but not
limited to offices and hotels, the disclosed adaptor has the
important function of enabling those installations to benefit from
this video transmission technique.
Details of the Coupling Network Circuitry
The earlier descriptions of the cooperating transceivers referred
to coupling network circuitry in functional terms. The preferred
embodiment of this circuitry is now presented in detail.
FIG. 6 shows the preferred embodiment of the coupling network of
the video source transceiver. The principal element of this network
is a transformer wound on a toroid core 71. There are three
isolated windings corresponding to the ports leading to the
telephone network wiring 72, the video signal amplifier 73, and the
control signal processing circuitry 74. The special winding method
shown for the phone line port serves to maximize its balance.
The low pass filter 75 on the port leading to the control signal
processing circuitry 74 blocks signals above the frequency used for
control signals. This blocks the video energy, preventing that
energy from disturbing the processing of the control signals, and
prevents loading of video signals on the telephone line.
There are different numbers of windings on the toroid core for the
three different ports (The number of windings shown are only for
purposes of illustration.) The turns ratios determine the impedance
matching between the telephone port and the other two ports.
Different ratios are needed because the video port and the control
signal port have different impedances at different frequencies.
The impedance matching for video signals is governed strictly by
the turns ratio between the telephone port and the video port. It
is independent of the windings on the IR port because the filter 75
prevents video energy from flowing towards that port.
The capacitor 77 serves as a high pass filter to block and present
a high impedance to DC and low-frequency energy, preventing any
disturbance of ordinary telephone communications at those
frequencies.
FIG. 7 shows the preferred embodiment of the coupling network of
the television transceiver. The principal element of this network
is again a transformer wound on a toroid core 80. There are three
isolated windings corresponding to the ports leading to the
telephone line 81, the television receiver 82, and the control
signal processing circuitry 83. The special winding method for the
telephone line shown earlier is not necessary because maximum
balance is not as important due to the lower energy level of the
video signals at this end.
The low pass filter 84 on the control signal port passes the 10.7
Mhz signal but blocks harmonics of 10.7 Mhz. These harmonics, whose
intelligence is redundant with the intelligence in the fundamental,
could potentially interfere with the video signals. The resulting
control signal passes on to both the telephone line and to the
television. To prevent loading down the video signal, the filter 84
also blocks video signals from the control signal port.
There are different numbers of windings on the toroid core 80 for
the three ports. (The number of windings shown are only for
purposes of illustration.) The turns ratios determine impedance
matching. Because the level of the control signal is high enough to
easily survive the influence of any impedance mismatch, the
impedance of the ports need only be properly matched at video
frequencies, and only between the telephone line port and the video
port.
The capacitor 85 serves as a high pass filter to block DC and
low-frequency energy and prevent any disturbance with ordinary
telephone communications at those frequencies.
It should be understood that various changes and modifications to
the preferred embodiment of the coupling network described above
will be apparent to those skilled in the art. For example, other
winding configurations are possible, including but not limited to
broadband multifilar configurations. These and other changes can be
made without departing from the spirit and scope of the
invention.
Details of the Control Signal Processing Circuitry
The earlier descriptions of the cooperating transceivers referred
to control signal processing circuitry in functional terms. The
preferred embodiment of this circuitry is now presented in
detail.
FIG. 8 shows the details of the control signal processing circuitry
in the television transceiver that detects infrared signals, and
translates them to RF energy. This circuitry consists of a
photodiode 101, a high-gain amplifier stage 102, a thresholded zero
crossing detector 103, and a gated oscillator 104. These elements
are arranged to produce a modulated RF carrier whose envelope is a
replica of the infrared signal waveform.
The RF carrier is coupled to the telephone line through the
coupling network 105. The coupling network shown in FIG. 8 is
designed only to feed control signals on to the network. The
coupling network of the preferred embodiment, which is designed to
include recovery of video signals from the wiring, is shown in FIG.
7 and was described earlier.
Photodiode 101 functions as a current source with current
proportional to the intensity of incident light within its spectral
passband. This photocurrent is converted to a voltage by resistor
110 and amplified by integrated circuit 111. Capacitors 112 and 113
reduce the low frequency gain of the amplifier stage to render the
receiver insensitive to ambient light sources, such as sunlight or
AC powered interior lighting with a nominal 120 Hz flicker rate.
Transistor 114 buffers and level-shifts the output of the
amplifier, and passes the signal to the zero crossing detector
section 103.
The output of the detector section 103 is a bi-level waveform that
corresponds to the received infrared signal. This output is high
when the input signal exceeds its long term average, and low
otherwise. Noise effects are suppressed by disabling the bi-level
signal except when the excursions of the input signal exceed a
fixed threshold. The bi-level waveform is fed to the oscillation
section to enable or disable the RF carrier, thus generating the
desired AM signal at an RF frequency. The output of comparator 122
is set high when the optical flux is greater than the long term
average, which is formed using an averaging time of 100 msec, as
determined by capacitor 127.
The noise condition is detected by comparator 123. It sets its
output low when the input signal is a fixed amount greater than the
long term average. This threshold is set so that noise will not
cause it to be exceeded. The threshold may be changed as desired by
altering the ratio of resistors 116 and 117 to provide different
levels of noise suppression.
Capacitor 126 causes a low output from comparator 123 to remain low
for a fixed period. Comparator 124 inverts this output, and
comparator 125 is used to merge that output with the output from
comparator 122. In this manner, the output exits to the oscillator
section without interruption when a genuine signal is present, and
dies off quickly when the signal disappears.
In the oscillator section, transistor 118 is wired as a Colpitts
oscillator with frequency determined primarily by capacitor 119 and
variable indicator 120. In the preferred embodiment, this frequency
is selected to be 10.7 Mhz because of the good availability of
tuning components at this frequency. When the oscillator is
disabled by comparator 125, an idle current of several milliamps is
drawn through the inductor and resistor 121. This idle current
provides rapid turn-on of the oscillator within a microsecond when
the oscillator is activated by comparator 125 going to a high
impedance state at its open-collector output.
FIG. 9 shows the control signal processing circuitry in the video
source transceiver that uses control signals recovered from the
network to recreate the infrared pattern detected by the television
transceiver. The circuitry consists of an RF amplifier/detector
131, threshold/driver circuitry 132, and an output LED 142.
The control signals are recovered from the telephone line by the
telephone coupling network 130. The coupling network shown in FIG.
9 is designed only to recover control signals from the network. The
coupling network of the preferred embodiment, which is designed to
include transmission of video signals onto the network, is shown in
FIG. 6 and was described earlier.
Signals recovered from the network pass through RF filter 133. This
filter, which is part of the coupling network, is a ceramic filter
with bandpass centered at 10.7 Mhz and a bandwidth of 280 khz. This
matches the characteristics of the RF signals generated by the
infrared signal processing circuitry described above.
The RF amplifier/detector 131 amplifies and envelope detects the
signals that pass through the filter. In the preferred embodiment,
this function is performed by an integrated circuit 134 of type
3089, which is commonly used as an IF amplifier in commercial FM
radios. The detected output is logarithmically related to the
amplitude of the RF input signal.
The detected output is buffered by Darlington transistor 140.
Comparator 141 provides threshold detection by comparing the
instantaneous envelope of the detected signal to the peak envelope
of the detected signal. The comparator turns on LED 142 whenever
the envelope exceeds a fixed percentage of the peak. Resistors 143
and 144 set the threshold of the transmitter: the LED will not be
driven on unless a minimum signal level at the input of the
integrated circuit 134 is exceeded.
While the foregoing has been provided with reference to one or more
preferred embodiments, various changes within the spirit of the
invention will be apparent to those of working skill in this
technical field. Thus, the invention should be considered as
limited only by the scope of the appended claims.
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